Fernando Rodriguez <frodriguez.develo...@outlook.com> [15-08-08 05:42]: > On Friday, August 07, 2015 7:01:29 PM Mick wrote: > > On Friday 07 Aug 2015 04:27:15 Fernando Rodriguez wrote: > > > On Thursday, August 06, 2015 6:18:59 PM meino.cra...@gmx.de wrote: > > > > Hi, > > > > > > > > for my tablet PC I used a used 32GB FAT32 formatted SDcard. The > > > > formatting was already done by the manufacturer. > > > > Then I screwed it up and had to do the partioning and formatting > > > > myself again. "No big deal", I thought -- and was wrong. > > > > Yes, the "thing" I got could be read and written. But it was > > > > DAMN slow in comparison to the original formatting. > > > > > > > > I googled and found a description, which described exactly, > > > > what I wanted: An optimal formatting for one big FAT32 partion. > > > > I did it again ;) and: TADA! The speed was back. > > > > LINK:http://zero1-st.blogspot.de/2012/05/formatting-fat32-volumes-larger-> > > > > > than.html > > > > > > > > Now I need the something identical but explained in a way > > > > that it can be successfully applied to any partion layout > > > > and any SDcard size. > > > > Currently the new SDcard has 64GB (yes, the tablet eats that size > > > > well :) and needs at least two partions: One FAT32 and one ext4. > > > > May be that I need a different layout later. > > > > > > > > To what aspect and "logic" do I have to keep my eyes on, when > > > > it comes partioning/formatting any SDcard size with any partion > > > > layout and any filesystem? > > > > > > > > Thank you very much in advance for any help! > > > > Best regards, > > > > Meino > > > > > > I wrote a long reply to this and it appears to have been swallowed by > > > /dev/null. > > > > > > SD cards don't have 128K blocks. Except for the very early ones (standard > > > capacity), they are divided in allocation units (AU) that are 1MB to 4MB > > > for SDHC and even larger for SDXC. The only way to get that value is by > > > reading a register in the card (so you can't do it in usermode on linux). > > > > > > The AUs are divided into Recording Units (RUs). The size of these can be > > > deduced from the card speed class (that's the number inside the C on the > > > label), and the card capacity. For class 2 and 4 if the card is less than > > > 1GB it's 16KB, otherwise it's 32KB. For class 6 it is 64KB, and for class > > > 10 it's 512KB. > > > > > > After an AU is erased you can write to any of the free RUs in any order in > > > blocks of 512 bytes sequentially (the block size is configurable by the > > > driver but 512 is the most common). But if you write to a nonfree RU then > > > all non- free RU get copied to a new AU. So the performance hit depends on > > > how many non-free RUs are in the AU when this happens. > > > > > > So to get the best performance you need to align the first FAT cluster on > > > an AU boundary and that the RUs used by the reserved sectors after the FAT > > > are free. This is not so easy from usermode because you can't get the AU > > > size and you can't erase the AU to make sure reserved sectors are free. > > > The Windows 7 and later format utility will do it if you don't partition > > > the card. The next best thing is to align it to an RU which should be > > > pretty easy. > > > > > > You could guess the AU size by writting blocks of RU size from the start > of > > > the card and timing it. Every time you hit the AU boundary there will be a > > > longer delay. > > > > > > For more details see the SD specification (chapter 4.13). > > > > > > https://www.sdcard.org/downloads/pls/ > > > > > > They also have formatter tools for Windows and OSX. I tried the Windows > > > version years ago but had problems with it (can't remember what). > > > > Excellent information Fernando, thank you! > > > > So there is no tool for me to use to read the AU/RU on the chip? > > > > > > The RU can be calculated from the card size and speed class, that's the > number > printed on the card label inside the C. I don't know of any tools to get the > AU and it looks like it's not exported to userspace so any such tool would > have to guess it. However, if you want to hack your kernel all it takes is > one > line on /usr/src/linux/drivers/mmc/core/debugfs.c. Add the following towards > the end of mmc_ios_show before the return statement: > > seq_printf(s, "au (sectors):\t%u\n", host->card->ssr.au); > > then you can do: > > cat /sys/kernel/debug/mmc0/ios > > Multiply the value by 512 to get the size in bytes. It can be up to 64MB. > > > > -- > Fernando Rodriguez >
Hi Fernando, I looked into the kernel ... but ... hmmmm ... for me it seems this is only for onboard mmc flash... which is often found on embedded linux boards. Or am I wrong? I am using a micro sdcard in a sdcard-reader plugged into an USB port of my Linux PC. (Later it will be inserted into the sdcard slot of my tablet PC...) I am asking just to prevent to make things screwed up. Have a nice sunday! :) Best regards, Meino
