Re: Memory replacement
On Tuesday 15 March 2011 01:29:19 John Watlington wrote: On Mar 14, 2011, at 3:18 PM, Arnd Bergmann wrote: Another effect is that the page size has increased by a factor of 8, from 2 or 4 KB to 16 or 32 KB. Writing data that as smaller than a page is more likely to get you into the worst case mentioned above. This is part of why FAT32 with 32 KB clusters still works reasonably well, but ext3 with 4 KB blocks has regressed so much. The explanation is simple: manufacturers moved to two-bit/cell (MLC) NAND Flash over a year ago, and six months ago moved to three-bit/cell (TLC) NAND Flash. Reliability went down, then went through the floor (I cannot recommend TLC for anything but write-once devices). You might have noticed this as an increase in the size of the erase block, as it doubled or more with the change. That, and the move to smaller structures (down to 25 nm) has of course reduced reliablility further, down to 2000 or so erase cycles per block, but that effect is unrelated to the file system being used. My point was that even if the card was done perfectly for FAT32 (maybe a write amplification of 2), the changes I described are pessimising ext3 (data from my head, easily off by an order of magnitude): drive block pageerase w-amplftn expected life sizesize sizecycles FAT ext3FAT ext3 2005 SLC 256 MB 64 KB 1 KB10 2 8 13 TB 3.2 TB 2005 MLC 512 MB 128 KB 2 KB1 2 16 2.5 TB 640 GB 2011 SLC 4 GB2 MB 8 KB5 2 512 100 TB 200 GB 2011 MLC 8 GB4 MB 16 KB 50002 102420 TB 40 GB 2011 TLC 16 GB 4 MB 16 KB 20002 102416 TB 32 GB The manufacturers have probably mitigated this slightly by using more spare blocks, better ECC and better GC over the years, but essentially your measurements are matching the theory. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sunday 13 March 2011, Mikus Grinbergs wrote: The tests have also helped expose other issues with things like sudden power off. In one case a SPO during a write would corrupt the card so badly it became useless. You could only recover them via a super secret tool from the manufacturer. Is there any sledgehammer process available to users without a super secret tool ? You can recover some cards by issueing an erase on the full drive. Unfortunately, this requires a patch to the SDHCI device driver, which is only now going into the kernel, I think it will be in 2.6.39. Issuing an erase (ioctl BLKDISCARD) also helps recover the performance on cards that get slower with increased internal fragmentation, but most cards use GC algorithms far too simple to get into that problem in the first place. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On 03/13/2011 06:34 PM, Mikus Grinbergs wrote: The tests have also helped expose other issues with things like sudden power off. In one case a SPO during a write would corrupt the card so badly it became useless. You could only recover them via a super secret tool from the manufacturer. Is there any sledgehammer process available to users without a super secret tool ? Wasn't just secret to users. They would not give us the info on how to do it either. It was vendor specific so not really worth the effort of trying to reverse engineer. -- Richard A. Smith rich...@laptop.org One Laptop per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sunday 13 March 2011, Richard A. Smith wrote: On 03/13/2011 01:21 PM, Arnd Bergmann wrote: There's a 2nd round of test(s) that runs during the manufacturing and burn-in phases. One is a simple firmware test to see if you can talk the card at all and then one runs at burn in. It doesn't have a minimum write size criteria but during the run there must not be any bit errors. ok. It does seem a bit crude, because many cards are not really suitable for this kind of file system when their wear leveling is purely optimized to the accesses defined in the sd card file system specification. If you did this on e.g. a typical Kingston card, it can have a write amplification 100 times higher than normal (FAT32, nilfs2, ...), so it gets painfully slow and wears out very quickly. Crude as they are they have been useful tests for us. Our top criteria is reliability. We want to ship the machines with a SD card thats going to last for the 5 year design life using the filesystem we ship. We tried to create an access pattern was the worst possible and the highest stress on the wear leveling system. I see. Using the 2 KB block size on ext3 as described in the Wiki should certainly do that, even on old cards that use 4 KB pages. I typically misalign the partition by a few sectors to get a similar effect, doubling the amount of internal garbage collection. I guess the real images use a higher block size, right? I had hoped that someone already correlated the GC algorithms with the requirements of specific file systems to allow a more systematic approach. At the time we started doing this testing none of the log structure filesystems were deemed to be mature enough for us to ship. So we didn't bother to try and torture test using them. If more precision tests were created that still allowed us to make a reasonable estimate of data write lifetime we would be happy to start using them. The tool that I'm working is git://git.linaro.org/people/arnd/flashbench.git It can be used to characterize a card in terms of its erase block size, number of open erase blocks, FAT optimized sections of the card, and possible access patterns inside of erase blocks, all by doing raw block I/O. Using it is currently a more manual process than I'd hope to make it for giving it to regular users. It also needs to be correlated to block access patterns from the file system. When you have that, it should be possible to accurately predict the amount of write amplification, which directly relates to how long the card ends up living. What I cannot determine right now is whether the card does static wear leveling. I have a Panasonic card that is advertized as doing it, but I haven't been able to pin down when that happens using timing attacks. Another thing you might be interested in is my other work on a block remapper that is designed to reduce the garbage collection by writing data in a log-structured way, similar to how some SSDs work internally. This will also do static wear leveling, as a way to improve the expected life by multiple orders of magnitude in some cases. https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashDeviceMapper lists some concepts I want to use, but I have done a lot of changes to the design that are not yet reflected in the Wiki. I need to talk to more people at the Embedded Linux Conference and Storage/FS summit in San Francisco to make sure I get that right. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Mar 13, 2011, at 6:34 PM, Mikus Grinbergs wrote: The tests have also helped expose other issues with things like sudden power off. In one case a SPO during a write would corrupt the card so badly it became useless. You could only recover them via a super secret tool from the manufacturer. Is there any sledgehammer process available to users without a super secret tool ? No. Such software does exist for every controller, but it doesn't necessarily use the SD interface as SD. I've encountered SD cards which will be recognized as a device when plugged in to a running XO-1 (though 'ls' of a filesystem on that SD card is corrupt) -- but 'fdisk' is ineffective when I want to write a new partition table (and 'fsck' appears to loop). Since otherwise I'd just have to throw the card away, I'd be willing to apply EXTREME measures to get such a card into a reusable (blank slate) condition. Cards that are in the state you describe are most likely dead due to running out of spare blocks. There is nothing that can be done to rehabilitate them, even using the manufacturer's secret code. In a disturbing trend, most of the cards I've returned for failure analysis in the past year have been worn out (and not just trashed meta-data due to a firmware error). Bummer, wad ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Monday 14 March 2011 19:50:27 John Watlington wrote: Cards that are in the state you describe are most likely dead due to running out of spare blocks. There is nothing that can be done to rehabilitate them, even using the manufacturer's secret code. In a disturbing trend, most of the cards I've returned for failure analysis in the past year have been worn out (and not just trashed meta-data due to a firmware error). Part of the explanation for this could be the fact that erase block sizes have rapidly increased. AFAIK, the original XO builtin flash had 128KB erase blocks, which is also a common size for 1GB SD and CF cards. Cards made in 2010 or later typically have erase blocks of 2 MB, and combine two of them into an allocation unit of 4 MB. This means that in the worst case (random access over the whole medium), the write amplification has increased by a factor of 32. Another effect is that the page size has increased by a factor of 8, from 2 or 4 KB to 16 or 32 KB. Writing data that as smaller than a page is more likely to get you into the worst case mentioned above. This is part of why FAT32 with 32 KB clusters still works reasonably well, but ext3 with 4 KB blocks has regressed so much. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Mar 14, 2011, at 3:18 PM, Arnd Bergmann wrote: On Monday 14 March 2011 19:50:27 John Watlington wrote: Cards that are in the state you describe are most likely dead due to running out of spare blocks. There is nothing that can be done to rehabilitate them, even using the manufacturer's secret code. In a disturbing trend, most of the cards I've returned for failure analysis in the past year have been worn out (and not just trashed meta-data due to a firmware error). Part of the explanation for this could be the fact that erase block sizes have rapidly increased. AFAIK, the original XO builtin flash had 128KB erase blocks, which is also a common size for 1GB SD and CF cards. Cards made in 2010 or later typically have erase blocks of 2 MB, and combine two of them into an allocation unit of 4 MB. This means that in the worst case (random access over the whole medium), the write amplification has increased by a factor of 32. Another effect is that the page size has increased by a factor of 8, from 2 or 4 KB to 16 or 32 KB. Writing data that as smaller than a page is more likely to get you into the worst case mentioned above. This is part of why FAT32 with 32 KB clusters still works reasonably well, but ext3 with 4 KB blocks has regressed so much. The explanation is simple: manufacturers moved to two-bit/cell (MLC) NAND Flash over a year ago, and six months ago moved to three-bit/cell (TLC) NAND Flash. Reliability went down, then went through the floor (I cannot recommend TLC for anything but write-once devices). You might have noticed this as an increase in the size of the erase block, as it doubled or more with the change. Cheers, wad ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sun, Mar 13, 2011 at 8:57 AM, Andrei Warkentin andr...@motorola.com wrote: Sorry to butt in, I think I'm missing most of the context herenevertheless... I'm curious, ignoring outer packaging and product names, if you look at cards with the same CID (i.e. same manfid/oemid/date/firmware and hw rev), do you get same performance characteristics? No. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sun, Mar 13, 2011 at 1:00 PM, C. Scott Ananian csc...@laptop.org wrote: On Sun, Mar 13, 2011 at 8:57 AM, Andrei Warkentin andr...@motorola.com wrote: Sorry to butt in, I think I'm missing most of the context herenevertheless... I'm curious, ignoring outer packaging and product names, if you look at cards with the same CID (i.e. same manfid/oemid/date/firmware and hw rev), do you get same performance characteristics? No. To elaborate: see bunnie's blog post (cited above) on how the CID is often forged or wrong. I've also personally witnessed a manufacturer's rep come to the factory floor to reprogram a compact flash card's internal microcontroller with new firmware. This did not update any externally visible information reported by the chip. I had to convince the manufacturer to leave their proprietary hardware on the factory floor in order to be able to verify that future units would have the correct firmware. (Granted, this was not an MMC unit, but I would be surprised if MMC vendors were significantly different in this regard.) If you've spent any time working with Chinese/Taiwanese OEMs, you will notice that version control methodologies are (in general) disappointingly lax. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sunday 13 March 2011 02:01:22 C. Scott Ananian wrote: On Sat, Mar 12, 2011 at 5:51 PM, Arnd Bergmann a...@arndb.de wrote: I've had four cards with a Sandisk label that had unusual characteristics and manufacturer/OEM IDs that refer to other companies, three Samsung (SM) and one unknown (BE, possibly lexar). In all cases, the Sandisk support has confirmed from photos that the cards are definitely fake. They also Please see the blog post I cited in the email immediately prior to yours, which discusses this situation precisely. Often the cards are not actually fake -- they may even be produced on the exact same equipment as the usual cards, but off the books during hours when the factory is officially closed. This sort of thing is very very widespread, and fakes can come even via official distribution channels. (Discussed in bunnie's post.) I am very familiar with bunnie's research, and have referenced it from my own page on the linaro wiki. I have also found Kingston cards with the exact same symptoms that triggered his original interest (very slow, manfid 0x41, oemid 42, low serial number). Another interesting case of a fake card I found had a Sandisk label and LEXAR in its MMC name field. Moreover, it actually contained copyrighted software that Lexar ships in their real cards. So what I'd assume is happening here is that the factory that produces the cards or Lexar had a graveyard shift where they were just printing Sandisk labels on the cards. You're giving the OEMs too much credit. As John says, unless you arrange for a special SKU, even the first source companies will give you whatever they've got cheap that day. It's pretty clear that they are moving to cheaper NAND chips when possible, and I also mentioned that. For the controller chips, I don't understand how they would save money by buying them on the spot market. On the contrary, using the smart controllers that Sandisk themselves make allows them to use even slower NAND chips and still qualify for a better nominal speed grade, while companies that don't have acess to decent controllers need to either use chips that are fast enough to make up for the bad GC algorithm or lie in their speed grades. How we deal with this is constant testing and getting notification from the manufacturer that they are changing the internals (unfortunately, we aren't willing to pay the premium to have a special SKU). Do you have test results somewhere publically available? We are currently discussing adding some tweaks to the linux mmc drivers to detect cards with certain features, and to do some optimizations in the block layer for common ones. http://wiki.laptop.org/go/NAND_Testing Ok, so the testing essentially means you create an ext2/3/4 file system and run tests on the file system until the card wears out, right? It does seem a bit crude, because many cards are not really suitable for this kind of file system when their wear leveling is purely optimized to the accesses defined in the sd card file system specification. If you did this on e.g. a typical Kingston card, it can have a write amplification 100 times higher than normal (FAT32, nilfs2, ...), so it gets painfully slow and wears out very quickly. I had hoped that someone already correlated the GC algorithms with the requirements of specific file systems to allow a more systematic approach. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sat, Mar 12, 2011 at 7:01 PM, C. Scott Ananian csc...@laptop.org wrote: On Sat, Mar 12, 2011 at 5:51 PM, Arnd Bergmann a...@arndb.de wrote: I've had four cards with a Sandisk label that had unusual characteristics and manufacturer/OEM IDs that refer to other companies, three Samsung (SM) and one unknown (BE, possibly lexar). In all cases, the Sandisk support has confirmed from photos that the cards are definitely fake. They also Please see the blog post I cited in the email immediately prior to yours, which discusses this situation precisely. Often the cards are not actually fake -- they may even be produced on the exact same equipment as the usual cards, but off the books during hours when the factory is officially closed. This sort of thing is very very widespread, and fakes can come even via official distribution channels. (Discussed in bunnie's post.) However, they have apparently managed to make them work well for random access by using some erase blocks as SLC (writing only the pages that carry the most significant bit in each cell) and by doing log structured writes in there, something that apparently others have not figured out yet. Also, as I mentioned, they consistenly use a relatively large number of open erase blocks. I've measured both effects on SD cards and USB sticks. You've been lucky. I believe you can get this level of sophistication only from companies that make the nand flash, the controller and the card: Sandisk, Samsung and Toshiba. Other brands that just get the controllers and the flash chips from whoever sells them cheaply (kingston, adata, panasonic, transcend, ...) apparently don't get the really good stuff. You're giving the OEMs too much credit. As John says, unless you arrange for a special SKU, even the first source companies will give you whatever they've got cheap that day. How we deal with this is constant testing and getting notification from the manufacturer that they are changing the internals (unfortunately, we aren't willing to pay the premium to have a special SKU). Do you have test results somewhere publically available? We are currently discussing adding some tweaks to the linux mmc drivers to detect cards with certain features, and to do some optimizations in the block layer for common ones. http://wiki.laptop.org/go/NAND_Testing But the testing wad is talking about is really *on the factory floor*: Regular sampling of chips as they come into the factory to ensure that the chips *you are actually about to put into the XOs* are consistent. Relying on manufacturing data reported by the chips is not reliable. --scott Sorry to butt in, I think I'm missing most of the context herenevertheless... I'm curious, ignoring outer packaging and product names, if you look at cards with the same CID (i.e. same manfid/oemid/date/firmware and hw rev), do you get same performance characteristics? Anyway, if you're curious about optimizing performance for certain cards, I'm curious to see your results, your tests and (if any) vendor recommendations. I'm collecting data and trying to re-validate some of the vendor suggestions for Toshiba eMMCs... in particular - splitting unaligned writes into an unaligned and aligned part. The only thing I can say now is that the more data I collect the less it makes sense :-). I'm resubmitting a change to MMC layer that allows creating block MMC quirks... Skipping the actual quirks as I'm trying to revalidate data taken by others and provide data I'm confident about, but you might be interested in the overall quirks support if you're thinking about adding your own. A ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On 03/13/2011 01:21 PM, Arnd Bergmann wrote: Do you have test results somewhere publically available? We are currently discussing adding some tweaks to the linux mmc drivers to detect cards with certain features, and to do some optimizations in the block layer for common ones. http://wiki.laptop.org/go/NAND_Testing Ok, so the testing essentially means you create an ext2/3/4 file system and run tests on the file system until the card wears out, right? The qualifying test is that the card must pass 3TB of writes with no errors. We run that on samples from the various mfg's. There's a 2nd round of test(s) that runs during the manufacturing and burn-in phases. One is a simple firmware test to see if you can talk the card at all and then one runs at burn in. It doesn't have a minimum write size criteria but during the run there must not be any bit errors. It does seem a bit crude, because many cards are not really suitable for this kind of file system when their wear leveling is purely optimized to the accesses defined in the sd card file system specification. If you did this on e.g. a typical Kingston card, it can have a write amplification 100 times higher than normal (FAT32, nilfs2, ...), so it gets painfully slow and wears out very quickly. Crude as they are they have been useful tests for us. Our top criteria is reliability. We want to ship the machines with a SD card thats going to last for the 5 year design life using the filesystem we ship. We tried to create an access pattern was the worst possible and the highest stress on the wear leveling system. If a card pases the 3TB abuse test then we are pretty certain its going to meet that goal. There were many cards that died very quickly. The tests have also helped expose other issues with things like sudden power off. In one case a SPO during a write would corrupt the card so badly it became useless. You could only recover them via a super secret tool from the manufacturer. I had hoped that someone already correlated the GC algorithms with the requirements of specific file systems to allow a more systematic approach. At the time we started doing this testing none of the log structure filesystems were deemed to be mature enough for us to ship. So we didn't bother to try and torture test using them. If more precision tests were created that still allowed us to make a reasonable estimate of data write lifetime we would be happy to start using them. -- Richard A. Smith rich...@laptop.org One Laptop per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
The tests have also helped expose other issues with things like sudden power off. In one case a SPO during a write would corrupt the card so badly it became useless. You could only recover them via a super secret tool from the manufacturer. Is there any sledgehammer process available to users without a super secret tool ? I've encountered SD cards which will be recognized as a device when plugged in to a running XO-1 (though 'ls' of a filesystem on that SD card is corrupt) -- but 'fdisk' is ineffective when I want to write a new partition table (and 'fsck' appears to loop). Since otherwise I'd just have to throw the card away, I'd be willing to apply EXTREME measures to get such a card into a reusable (blank slate) condition. mikus ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Mar 11, 2011, at 5:35 AM, Arnd Bergmann wrote: I've tested around a dozen media from them, and while you are true that they use rather different algorithms and NAND chips inside, all of them can write to at least 5 erase blocks before getting into garbage collection, which is really needed for ext3 file systems. Contrast this with Kingston cards, which all use the same algorithm and can only write data linearly to one erase block at a time, resulting in one or two orders of magnitude higher internal write amplification. Most other vendors are somewhere inbetween, and you sometimes get fake cards that don't do what you expect, such a a bunch of Samsung microSDHC cards thaI have I which are labeled Sandisk on the outside. Those aren't fakes. That is what I'm trying to get across. I've also seen some really cheap noname cards outperform similar-spec'd sandisk card, both regarding maximum throughput and the garbage collection algorithms, but you can't rely on that. My point is that you can't rely on Sandisk either. I've been in discussion with both Sandisk and Adata about these issues, as well as constantly testing batches of new SD cards from all major vendors. Unless you pay a lot extra and order at least 100K, you have no control over what they give you. They don't just change NAND chips, they change the controller chip and its firmware. Frequently. And they don't update either the SKU number, part marking or the identification fields available to software.The manufacturing batch number printed on the outside is the only thing that changes. How we deal with this is constant testing and getting notification from the manufacturer that they are changing the internals (unfortunately, we aren't willing to pay the premium to have a special SKU). Cheers, wad ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
Canonical related blog post: http://www.bunniestudios.com/blog/?p=918 Mandatory reading for anyone who has to deal with flash memory. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Friday 11 March 2011 18:28:49 John Watlington wrote: On Mar 11, 2011, at 5:35 AM, Arnd Bergmann wrote: I've tested around a dozen media from them, and while you are true that they use rather different algorithms and NAND chips inside, all of them can write to at least 5 erase blocks before getting into garbage collection, which is really needed for ext3 file systems. Contrast this with Kingston cards, which all use the same algorithm and can only write data linearly to one erase block at a time, resulting in one or two orders of magnitude higher internal write amplification. Most other vendors are somewhere inbetween, and you sometimes get fake cards that don't do what you expect, such a a bunch of Samsung microSDHC cards thaI have I which are labeled Sandisk on the outside. Those aren't fakes. That is what I'm trying to get across. I've had four cards with a Sandisk label that had unusual characteristics and manufacturer/OEM IDs that refer to other companies, three Samsung (SM) and one unknown (BE, possibly lexar). In all cases, the Sandisk support has confirmed from photos that the cards are definitely fake. They also explained that all authentic cards (possibly fake ones as well, but I have not seen them) will be labeled Made in China, not Made in Korea or Made in Taiwan as my fake ones, and that the authentic microSD cards have the serial number on the front side, not on the back. I've also seen some really cheap noname cards outperform similar-spec'd sandisk card, both regarding maximum throughput and the garbage collection algorithms, but you can't rely on that. My point is that you can't rely on Sandisk either. I've been in discussion with both Sandisk and Adata about these issues, as well as constantly testing batches of new SD cards from all major vendors. Unless you pay a lot extra and order at least 100K, you have no control over what they give you. They don't just change NAND chips, they change the controller chip and its firmware. Frequently. And they don't update either the SKU number, part marking or the identification fields available to software.The manufacturing batch number printed on the outside is the only thing that changes. I agree that you cannot rely on specific behavior to stay the same with any vendor. One thing I noticed for instance is that many new Sandisk cards are using TLC (three level cell) NAND, which is inherently slower and cheaper than the regular two-level MLC used in older cards or those from other vendors. However, they have apparently managed to make them work well for random access by using some erase blocks as SLC (writing only the pages that carry the most significant bit in each cell) and by doing log structured writes in there, something that apparently others have not figured out yet. Also, as I mentioned, they consistenly use a relatively large number of open erase blocks. I've measured both effects on SD cards and USB sticks. I believe you can get this level of sophistication only from companies that make the nand flash, the controller and the card: Sandisk, Samsung and Toshiba. Other brands that just get the controllers and the flash chips from whoever sells them cheaply (kingston, adata, panasonic, transcend, ...) apparently don't get the really good stuff. How we deal with this is constant testing and getting notification from the manufacturer that they are changing the internals (unfortunately, we aren't willing to pay the premium to have a special SKU). Do you have test results somewhere publically available? We are currently discussing adding some tweaks to the linux mmc drivers to detect cards with certain features, and to do some optimizations in the block layer for common ones. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Sat, Mar 12, 2011 at 5:51 PM, Arnd Bergmann a...@arndb.de wrote: I've had four cards with a Sandisk label that had unusual characteristics and manufacturer/OEM IDs that refer to other companies, three Samsung (SM) and one unknown (BE, possibly lexar). In all cases, the Sandisk support has confirmed from photos that the cards are definitely fake. They also Please see the blog post I cited in the email immediately prior to yours, which discusses this situation precisely. Often the cards are not actually fake -- they may even be produced on the exact same equipment as the usual cards, but off the books during hours when the factory is officially closed. This sort of thing is very very widespread, and fakes can come even via official distribution channels. (Discussed in bunnie's post.) However, they have apparently managed to make them work well for random access by using some erase blocks as SLC (writing only the pages that carry the most significant bit in each cell) and by doing log structured writes in there, something that apparently others have not figured out yet. Also, as I mentioned, they consistenly use a relatively large number of open erase blocks. I've measured both effects on SD cards and USB sticks. You've been lucky. I believe you can get this level of sophistication only from companies that make the nand flash, the controller and the card: Sandisk, Samsung and Toshiba. Other brands that just get the controllers and the flash chips from whoever sells them cheaply (kingston, adata, panasonic, transcend, ...) apparently don't get the really good stuff. You're giving the OEMs too much credit. As John says, unless you arrange for a special SKU, even the first source companies will give you whatever they've got cheap that day. How we deal with this is constant testing and getting notification from the manufacturer that they are changing the internals (unfortunately, we aren't willing to pay the premium to have a special SKU). Do you have test results somewhere publically available? We are currently discussing adding some tweaks to the linux mmc drivers to detect cards with certain features, and to do some optimizations in the block layer for common ones. http://wiki.laptop.org/go/NAND_Testing But the testing wad is talking about is really *on the factory floor*: Regular sampling of chips as they come into the factory to ensure that the chips *you are actually about to put into the XOs* are consistent. Relying on manufacturing data reported by the chips is not reliable. --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Friday 11 March 2011, John Watlington wrote: On Mar 9, 2011, at 2:23 PM, Arnd Bergmann wrote: On Wednesday 09 March 2011 17:31:24 Kevin Gordon wrote: go, no-go, spend the extra pennies and get a Class 4/6/8/10 Note that Class 8 does not exist (except fakes) and class 10 is usually not faster than class 6 if you run ext3 on it. Also, a Sandisk card is usually faster than a card from most other manufacturers even if they are one class faster nominally. I'll call BS on that claim. Sandisk cards are all over the map, depending on the controller used internally.Please understand that these manufacturers change controllers all the time --- tests results from nine months ago are invalid. I've tested around a dozen media from them, and while you are true that they use rather different algorithms and NAND chips inside, all of them can write to at least 5 erase blocks before getting into garbage collection, which is really needed for ext3 file systems. Contrast this with Kingston cards, which all use the same algorithm and can only write data linearly to one erase block at a time, resulting in one or two orders of magnitude higher internal write amplification. Most other vendors are somewhere inbetween, and you sometimes get fake cards that don't do what you expect, such a a bunch of Samsung microSDHC cards thaI have I which are labeled Sandisk on the outside. I've also seen some really cheap noname cards outperform similar-spec'd sandisk card, both regarding maximum throughput and the garbage collection algorithms, but you can't rely on that. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On 10 March 2011 05:51, Paul Fox p...@laptop.org wrote: kevin wrote: and having my anti-static wrist guard properly attached - advice please: go, no-go, spend the extra pennies and get a Class 4/6/8/10. All I know for sure is the 2GiB card in there has to be replaced. There are progressively if you're using the machine a lot, and you have the pennies, the difference a faster card makes will be noticeable. I assume that this is just for personal use and not for deployment. A few months ago I enquired about the possibility of getting Class 6 cards in our deployment XOs, and was informed that none of the Class 6 cards tested could pass reliability tests. That sort of thing becomes critical if you want the XO to last for five years in the field. Sridhar ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Mar 9, 2011, at 2:23 PM, Arnd Bergmann wrote: On Wednesday 09 March 2011 17:31:24 Kevin Gordon wrote: go, no-go, spend the extra pennies and get a Class 4/6/8/10 Note that Class 8 does not exist (except fakes) and class 10 is usually not faster than class 6 if you run ext3 on it. Also, a Sandisk card is usually faster than a card from most other manufacturers even if they are one class faster nominally. I'll call BS on that claim. Sandisk cards are all over the map, depending on the controller used internally.Please understand that these manufacturers change controllers all the time --- tests results from nine months ago are invalid. See https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashCardSurvey for a list of many cards. Go for a brand that has a larger number of open segments. Also make sure that the partition is aligned to 4 MB, otherwise you waste half the performance and expected life. We align our images to 8 MB boundaries, as 4MB isn't enough for some cards. Since fs-update installs the partition table as well as the partition images, this happens automatically. Cheers, wad ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
Mikus and James and the gang: OK, the little 8GiB microSD card inserted into an SD adapter, inserted into the external SD slot, passed the dir test that James said to perform at OFW. Didnt complain. However, it is a Class 2 Sandisk card, so it might not really be the right way to go. Before I do the surgery, armed with silver heat sink paste, and being very careful about pressure on the m/b, and having my anti-static wrist guard properly attached - advice please: go, no-go, spend the extra pennies and get a Class 4/6/8/10. All I know for sure is the 2GiB card in there has to be replaced. There are progressively more and red squares appearing on every refresh, and since this is a 'contributors machine' that I screw up regularly testing a billion USB contraptions, I reload almost every day that I use it :-) Thanks gents. KG On Sun, Mar 6, 2011 at 4:06 PM, Mikus Grinbergs mi...@bga.com wrote: how to upgrade the SD card ? All you have to do is stick the new card in, then perform the 'fs-update' (with an appropriate-sized .zd image). The ENTIRE SD-card-content will be written-over-anew, including the partition table. The catch is that the micro-SD card is beneath the heat spreader - and once you replace the card, you have to make sure that the heat spreader has thermal contact with the CPU chip. [I suspect that too much physical pressure at the CPU chip might have contributed to the #10314 failures of some pre-production XO-1.5 motherboards.] a fresh new 8GiB micro-SD card I had good luck with a 8GiB micro-SD card in the 2009 XO-1.5 I had (but that system eventually stopped working - I don't know if my having put in a different micro-SD card had any relationship to that failure). What appears to matter most with the micro-SD card is its SPEED (it would take a heck of a lot of Journal entries to fill even a 4GiB card). There was a discussion on the devel list a long while ago about the transfer speeds measured on the XO-1.5 with several different cards -- apparently NOT ALL the available cards met OLPC reliability specs. mikus ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
advice please: go, no-go, spend the extra pennies and get a Class 4/6/8/10 Go. I was interested in having a higher-performing XO-1.5 -- so the card I bought back then was a class 6. It is likely the micro-SD card you have now is a class 2 -- so your new card (Sandisk has good reputation for reliable SD cards) will perform the same as what you are used to. Since your existing card is deteriorating - go ahead and replace it. mikus ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
kevin wrote: Mikus and James and the gang: OK, the little 8GiB microSD card inserted into an SD adapter, inserted into the external SD slot, passed the dir test that James said to perform at OFW. Didnt complain. However, it is a Class 2 Sandisk card, so it might not really be the right way to go. Before I do the surgery, armed with silver heat sink paste, and being very careful about pressure on the m/b, no paste is used when the laptops are manufactured, and none should really be necessary afterward. it's true that later head spreaders were modified (with an extra attachment point) to ensure proper contact with the cpu, but you can help ensure the same thing by gently bending each of the flat feet that holds a screw slightly downward. (not the ones that _don't_ hold a screw -- leave those flat.) bending the mounting tabs down will cause the center of the heat spreader to bow towards the motherboard when the screws flatten out the feet. there's a picture here: http://lists.laptop.org/pipermail/devel/attachments/20091103/4e777bb2/attachment-0001.pdf (it's an attachment to this devel message: http://lists.laptop.org/pipermail/devel/2009-November/026110.html ) and having my anti-static wrist guard properly attached - advice please: go, no-go, spend the extra pennies and get a Class 4/6/8/10. All I know for sure is the 2GiB card in there has to be replaced. There are progressively if you're using the machine a lot, and you have the pennies, the difference a faster card makes will be noticeable. paul more and red squares appearing on every refresh, and since this is a 'contributors machine' that I screw up regularly testing a billion USB contraptions, I reload almost every day that I use it :-) Thanks gents. and ladies, i'm sure. =- paul fox, p...@laptop.org ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Wednesday 09 March 2011 17:31:24 Kevin Gordon wrote: go, no-go, spend the extra pennies and get a Class 4/6/8/10 Note that Class 8 does not exist (except fakes) and class 10 is usually not faster than class 6 if you run ext3 on it. Also, a Sandisk card is usually faster than a card from most other manufacturers even if they are one class faster nominally. See https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashCardSurvey for a list of many cards. Go for a brand that has a larger number of open segments. Also make sure that the partition is aligned to 4 MB, otherwise you waste half the performance and expected life. Arnd ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
Also make sure that the partition is aligned to 4 MB, otherwise you waste half the performance and expected life. I do this for every SD card onto which I myself write the partition table. But I think the .zd files re-write the WHOLE SD card (including its partition table). If that is true, then the person replacing the SD card has no control over where the partitions get placed -- only the person who created the .zd file can customize that partition table. mikus ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Wed, Mar 09, 2011 at 03:15:12PM -0600, Mikus Grinbergs wrote: But I think the .zd files re-write the WHOLE SD card (including its partition table). If that is true, then the person replacing the SD card has no control over where the partitions get placed -- only the person who created the .zd file can customize that partition table. This is true. -- James Cameron http://quozl.linux.org.au/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
On Wed, Mar 09, 2011 at 11:31:24AM -0500, Kevin Gordon wrote: OK, the little 8GiB microSD card inserted into an SD adapter, inserted into the external SD slot, passed the dir test that James said to perform at OFW. Didnt complain. Good. You must test again if you change cards, by the way. However, it is a Class 2 Sandisk card, so it might not really be the right way to go. You can fs-update it in the external slot, and this will give you a good indication of write performance in two ways; the flickering of the storage LED during the fs-update, and the total time shown at the end of the fs-update. ok devalias fsdisk /sd/disk@1:0 ok fs-update ... Then you can boot it, and the laptop should boot from the external card and not use the internal card. Before I do the surgery, armed with silver heat sink paste, I've never tried heat sink paste, I don't know if it is recommended, but there's a thermal test in OpenFirmware you might try before and after. ok test /switches It instructs you to close the laptop, after which you should open it, then it asks for e-book configuration. Note the temperature rise. Note your environment temperature so that you can reproduce the test reliably. advice please: go, no-go, spend the extra pennies and get a Class 4/6/8/10. A faster card is certainly worth getting, but Class 4/6/8/10 doesn't really indicate how fast it will be. The definition of these classes corresponds to sequential write rate by a camera to a FAT filesystem, not random writes to an ext3 filesystem! All I know for sure is the 2GiB card in there has to be replaced. There are progressively more and red squares appearing on every refresh, I don't agree with your assessment. It might easily be another defect, and not the card itself. If it were in my hands I would do more write testing on the internal card, using Tiny Core booted from USB. You might defer the surgery and instead use the external slot for a while. -- James Cameron http://quozl.linux.org.au/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
Hi, On Sun, Mar 06 2011, Kevin Gordon wrote: Might someone be able to point me to the place where one can get instructions on how to upgrade the SD card from an old XO 1.5 currently with 2GiB, to a fresh new 8GiB micro-SD card? Just: wget http://build.laptop.org/10.1.3/xo-1.5/os860/os860-8g.zd ok fs-update os860-8g.zd (OFW does the formatting for you.) - Chris. -- Chris Ball c...@laptop.org http://printf.net/ One Laptop Per Child ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Memory replacement
how to upgrade the SD card ? All you have to do is stick the new card in, then perform the 'fs-update' (with an appropriate-sized .zd image). The ENTIRE SD-card-content will be written-over-anew, including the partition table. The catch is that the micro-SD card is beneath the heat spreader - and once you replace the card, you have to make sure that the heat spreader has thermal contact with the CPU chip. [I suspect that too much physical pressure at the CPU chip might have contributed to the #10314 failures of some pre-production XO-1.5 motherboards.] a fresh new 8GiB micro-SD card I had good luck with a 8GiB micro-SD card in the 2009 XO-1.5 I had (but that system eventually stopped working - I don't know if my having put in a different micro-SD card had any relationship to that failure). What appears to matter most with the micro-SD card is its SPEED (it would take a heck of a lot of Journal entries to fill even a 4GiB card). There was a discussion on the devel list a long while ago about the transfer speeds measured on the XO-1.5 with several different cards -- apparently NOT ALL the available cards met OLPC reliability specs. mikus ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
