It sounds like people are missing the forest for the trees. Some of us have been successfully RAIDing/deploying storage for years on everything from IDE vinum to SCSI XFS and beyond without ECC. We use ZFS today because of its featureset. Data integrity checking through checksumming is just one of those features which would have mitigated some issues that other file systems have historically failed to do. (Otherwise we should all be happy with existing journaling filesystems on a soft or hard RAID). ECC just adds another layer of mitigation (and even in a less-implementation-specific way like how ZFS may 'prefer' raw device access instead of whatever storage abstraction the controller is presenting). Asserting that ECC is "required" has about the same logic to it (and I would say less logic to it) than asserting a 3ware controller with raw jbod passthrough is "required".
On Sat, Apr 12, 2014 at 7:46 AM, Bayard Bell <buffer.g.overf...@gmail.com> wrote: > Jason, > > Although I moved from OS X to illumos as a primary platform precisely > because of ZFS (I ended up posting to the original list about the demise of > the project because I happened to be doing an install the week Apple people > the plug), I've spent enough time with OS X, including debugging storage > interop issues with NexentaStor in significant commercial deployments, that > it's risible to suggest I have zero knowledge of the platform and even more > risible to imply that the role of ECC in ZFS architecture is here somehow > fundamentally a matter of platform variation. I've pointed to a Solaris > engineer showing core dumps from non-ECC RAM and reporting data corruption > as a substantiated instance of ECC problems, and I've pointed to references > to how ECC serves as a point of reference from one of its co-creators. I've > explained that ECC in ZFS should be understood in terms of the scale it > allow and the challenges that creates for data integrity protection, and > I've tried to contrast the economics of ECC to what I take to be a less > compelling alternative sketched out by the Mdison paper. At the same time > I've said that ECC use is genereally assumed in ZFS, I've allowed that doing > so is a question of an incremental cost against the value of your data and > costs to replace it. > > I don't understand why you've decided to invest so much in arguing that ECC > is so completely marginal a data integrity measure that you can't have a > reasonable discussion about what gets people to different conclusions and > feel the need to be overtly dismissive of the professionalism and expertise > of those who come to fundamentally different conclusions, but clearly > there's not going to be a dialogue on this. My only interest in posting at > this point is so that people on this list at least have a clear statement of > both ends of the argument and can judge for themselves. > > Regards, > Bayard > > > On 12 April 2014 11:44, Jason Belec <jasonbe...@belecmartin.com> wrote: >> >> Hhhhmmmmm, oh I get it, you have zero knowledge of the platform this list >> represents. No worries, appreciate your time clearing that up. >> >> >> >> -- >> Jason Belec >> Sent from my iPad >> >> On Apr 12, 2014, at 6:26 AM, Bayard Bell <buffer.g.overf...@gmail.com> >> wrote: >> >> Jason, >> >> If you think I've said anything about the sky falling or referenced a >> wiki, you're responding to something other than what I wrote. I see no need >> for further reply. >> >> Cheers, >> Bayard >> >> >> On 11 April 2014 22:36, Jason Belec <jasonbe...@belecmartin.com> wrote: >>> >>> Excellent. If you feel this is necessary go for it. Those that have >>> systems that don't have ECC should just run like the sky is falling by your >>> point view. That said, I can guarantee non of the systems I have under my >>> care have issues. How do I know? Well the data is tested/compared at regular >>> intervals. Maybe I'm the luckiest guy ever, where is that lottery ticket. Is >>> ECC better, possibly, probably in heavy load environments, no data has been >>> provided to back this up. Especially nothing in the context of what most >>> users needs are at least here in the Mac space. Which ECC? Be specific. They >>> are not all the same. Just like regular RAM are not all the same. Just like >>> HDDs are not all the same. Fear mongering is wonderful and easy. Putting >>> forth a solution guaranteed to be better is what's needed now. Did you >>> actually reference a wiki? Seriously? A document anyone can edit to suit >>> there view? I guess I come from a different era. >>> >>> >>> Jason >>> Sent from my iPhone 5S >>> >>> On Apr 11, 2014, at 5:09 PM, Bayard Bell <buffer.g.overf...@gmail.com> >>> wrote: >>> >>> If you want more of a smoking gun report on data corruption without ECC, >>> try: >>> >>> https://blogs.oracle.com/vlad/entry/zfs_likes_to_have_ecc >>> >>> This view isn't isolated in terms of what people at Sun thought or what >>> people at Oracle now think. Trying googling for "zfs ecc >>> site:blogs.oracle.com", and you'll find a recurring statement that ECC >>> should be used even in home deployment, with maybe one odd exception. >>> >>> The Wikipedia article, correctly summarising the Google study, is plain >>> in saying not that extremely high error rates are common but that error >>> rates are highly variable in large-sample studies, with some systems seeing >>> extremely high error rates. ECC gives a significant assurance based on an >>> incremental cost, so what's your data worth? You're not guaranteed to be >>> screwed by not using ECC (and the Google paper doesn't say this either), but >>> you are assuming risks that ECC mitigates. Look at the above blog, however: >>> even DIMMs that are high-quality but non-ECC can go wrong and result in >>> nasty system corruption. >>> >>> What generally protects you in terms of pool integrity is metadata >>> redundancy on top of integrity checks, but if you flip bits on metadata >>> in-core before writing redundant copies, well, that's a risk to pool >>> integrity. >>> >>> I also think it's mistaken to say this is distinctly a problem with ZFS. >>> Any "next-generation" filesystem that provides protections against on-disk >>> corruption via checksums ends up with a residual risk focus on making sure >>> that in-core data integrity is robust. You could well have those problems on >>> the pools you've deployed, and there are a lot of situations in you'd never >>> know and quite a lot (such as most of the bits in a photo or MP3) where >>> you'd never notice low rates of bit-flipping. The fact that you haven't >>> noticed doesn't equate to there being no problems in a strict sense, it's >>> far more likely that you've been able to tolerate the flipping that's >>> happened. The guy at Sun with the blog above got lucky: he was running >>> high-quality non-ECC RAM, and it went pear-shaped, at least for metadata >>> cancer, quite quickly, allowing him to recover by rolling back snapshots. >>> >>> Take a look out there, and you'll find people who are very confused about >>> the risks and available mitigations. I found someone saying that there's no >>> problem with more traditional RAID technologies because disks have CRCs. By >>> comparison, you can find Bonwick, educated as a statistician, talking about >>> SHA256 collisions by comparison to undetected ECC error rates and >>> introducing ZFS data integrity safeguards by way of analogy to ECC. That's >>> why the large-sample studies are interesting and useful: none of this >>> technology makes data corruption impossible, it just goes to extreme length >>> to marginalise the chances of those events by addressing known sources of >>> errors and fundamental error scenarios--in-core is so core that if you >>> tolerate error there, those errors will characterize systematic behaviour >>> where you have better outcomes reasonably available (and that's >>> **reasonably** available, I would suggest, in a way that the Madison paper's >>> recommendation to make ZFS buffers magical isn't). CRC-32 does a great job >>> detecting bad sectors and preventing them from being read back, but SHA256 >>> in the right place in a system detects errors that a well-conceived vdev >>> topology will generally make recoverable. That includes catching cases where >>> an error isn't caught by CRC-32, which may be a rare result, but when you've >>> got the kind of data densities that ZFS can allow, you're rolling the dice >>> often enough that those results become interesting. >>> >>> ECC is one of the most basic steps to take, and if you look at the >>> architectural literature, that's how it's treated. If you really want to be >>> in on the joke, find the opensolaris zfs list thread from 2009 where someone >>> asks about ECC, and someone else jumps in to remark on how VirtualBox can be >>> poison for pool integrity for reasons rehearsed in my last post. >>> >>> Cheers, >>> Bayard >>> >>> On 1 April 2014 12:04, Jason Belec <jasonbe...@belecmartin.com> wrote: >>>> >>>> ZFS is lots of parts, in most cases lots of cheap unreliable parts, >>>> refurbished parts, yadda yadda, as posted on this thread and many, many >>>> others, any issues are probably not ZFS but the parts of the whole. Yes, it >>>> could be ZFS, after you confirm that all the parts ate pristine, maybe. >>>> >>>> My oldest system running ZFS is an Mac Mini Intel Core Duo with 3GB RAM >>>> (not ECC) it is the home server for music, tv shows, movies, and some >>>> interim backups. The mini has been modded for ESATA and has 6 drives >>>> connected. The pool is 2 RaidZ of 3 mirrored with copies set at 2. Been >>>> running since ZFS was released from Apple builds. Lost 3 drives, eventually >>>> traced to a new cable that cracked at the connector which when hot enough >>>> expanded lifting 2 pins free of their connector counter parts resulting in >>>> errors. Visually almost impossible to see. I replaced port multipliers, >>>> Esata cards, RAM, mini's, power supply, reinstalled OS, reinstalled ZFS, >>>> restored ZFS data from backup, finally to find the bad connector end one >>>> because it was hot and felt 'funny'. >>>> >>>> Frustrating, yes, educational also. The happy news is, all the data was >>>> fine, wife would have torn me to shreds if photos were missing, music was >>>> corrupt, etc., etc.. And this was on the old out of date but stable ZFS >>>> version we Mac users have been hugging onto for dear life. YMMV >>>> >>>> Never had RAM as the issue, here in the mad science lab across 10 >>>> rotating systems or in any client location - pick your decade. However I >>>> don't use cheap RAM either, and I only have 2 Systems requiring ECC >>>> currently that don't even connect to ZFS as they are both XServers with >>>> other lives. >>>> >>>> >>>> >>>> -- >>>> Jason Belec >>>> Sent from my iPad >>>> >>>> On Apr 1, 2014, at 12:13 AM, Daniel Becker <razzf...@gmail.com> wrote: >>>> >>>> On Mar 31, 2014, at 7:41 PM, Eric Jaw <naisa...@gmail.com> wrote: >>>> >>>> I started using ZFS about a few weeks ago, so a lot of it is still new >>>> to me. I'm actually not completely certain about "proper procedure" for >>>> repairing a pool. I'm not sure if I'm supposed to clear the errors after >>>> the >>>> scrub, before or after (little things). I'm not sure if it even matters. >>>> When I restarted the VM, the checksum counts cleared on its own. >>>> >>>> >>>> The counts are not maintained across reboots. >>>> >>>> >>>> On the first scrub it repaired roughly 1.65MB. None on the second scub. >>>> Even after the scrub there were still 43 data errors. I was expecting they >>>> were going to go away. >>>> >>>> >>>>> errors: 43 data errors, use '-v' for a list >>>> >>>> >>>> What this means is that in these 43 cases, the system was not able to >>>> correct the error (i.e., both drives in a mirror returned bad data). >>>> >>>> >>>> This is an excellent question. They're in 'Normal' mode. I remember >>>> looking in to this before and decided normal mode should be fine. I might >>>> be >>>> wrong. So thanks for bringing this up. I'll have to check it out again. >>>> >>>> >>>> The reason I was asking is that these symptoms would also be consistent >>>> with something outside the VM writing to the disks behind the VM’s back; >>>> that’s unlikely to happen accidentally with disk images, but raw disks are >>>> visible to the host OS as such, so it may be as simple as Windows deciding >>>> that it should initialize the “unformatted” (really, formatted with an >>>> unknown filesystem) devices. Or it could be a raid controller that stores >>>> its array metadata in the last sector of the array’s disks. >>>> >>>> >>>> memtest86 and memtest86+ for 18 hours came out okay. I'm on my third >>>> scrub and the number or errors has remained at 43. Checksum errors continue >>>> to pile up as the pool is getting scrubbed. >>>> >>>> I'm just as flustered about this. Thanks again for the input. >>>> >>>> >>>> Given that you’re seeing a fairly large number of errors in your scrubs, >>>> the fact that memtest86 doesn’t find anything at all very strongly suggests >>>> that this is not actually a memory issue. >>>> >>>> -- >>>> >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "zfs-macos" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to zfs-macos+unsubscr...@googlegroups.com. >>>> For more options, visit https://groups.google.com/d/optout. >>> >>> >>> -- >>> >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "zfs-macos" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to zfs-macos+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >>> -- >>> >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "zfs-macos" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to zfs-macos+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >> >> >> -- >> >> --- >> You received this message because you are subscribed to the Google Groups >> "zfs-macos" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to zfs-macos+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> >> -- >> >> --- >> You received this message because you are subscribed to the Google Groups >> "zfs-macos" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to zfs-macos+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. > > > -- > > --- > You received this message because you are subscribed to the Google Groups > "zfs-macos" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to zfs-macos+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- --- You received this message because you are subscribed to the Google Groups "zfs-macos" group. 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