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Ask Slashdot: How Do SSDs Die?
First time accepted submitter kfsone writes "I've experienced, first-hand, some of the ways in which spindle disks die, but either I've yet to see an SSD die or I'm not looking in the right places. Most of my admin-type friends have theories on how an SSD dies but admit none of them has actually seen commercial grade drives die or deteriorate. In particular, the failure process seems like it should be more clinical than spindle drives. If you have X many of the same SSD drive and none of them suffer manufacturing defects, if you repeat the same series of operations on them they should all die around the same time. If that's correct, then what happens to SSDs in RAID? Either all your drives will start to fail together or at some point, your drives will become out of sync in-terms of volume sizing. So, have you had to deliberately EOL corporate grade SSDs? Do they die with dignity or go out with a bang?"
I had 2 out of 5 SSDs fail (OCZ) with CRC errors, I'm guessing faulty cells.
In general, if the SSD in question has a well-designed controller (Intel, SandForce), then write performance will begin to drop off as bad blocks start to accumulate on the drive. Eventually, wear levelling and write cycles have taken their toll, and the disk can no longer write at all. At this point, the controller does all it can: it effectively becomes a read-only disk. It should operate in this mode until else something catastrophic (tin migration, capacitor failure, etc.) keeps the entire drive from working.
BTW - I haven't seen this either, but that's the degradation profile that's been presented to me in several presentations by the folks making SSD drives and controllers. (Intel had a great one a few years back - don't have a link to it handy, though...)
"The future's good and the present is nothing to sneeze at." - Roblimo's last
The drives will shrink down to nothing. I believe that the drive controller considers a sector dead after 100,000 writes.
Filesystems, generally speaking, aren't resilient to the underlying disk geometry changing after they've been laid down. There's reserved space to replace bad cells as they start to die, but the disk won't shrink. Eventually, though, you get parts of the disk dying in an unrecoverable way and the drive is toast.
It was my understanding that for traditional drives in a RAID you don't want to get all the same type of drive all made around the same time since they will fail around the same time too. Same would apply to SSDs.
Never heard of that. I've got about 450 servers each with a raid1 and raid10 array of physical disks. We always buy everything together, including all the disks. If one fails we get alerts from the monitoring software and get a technician to the site that night for a disk replacement. I think I've seen one incident in the past 14 years I've been in this department where more than one disk failed at a time.
My thought on buying them separately is that you run the risk of getting devices with different firmware levels or other manufacturer revisions which would be less than ideal when raided together. Not to mention you have a mess for warranty management. We replace systems (disks included) when the 4 year warranty expires.
All three of the commercial grade SSD failures I've cleaned up after (I do PostgreSQL data recovery) just died. No warning, no degrading in SMART attributes; works one minute, slag heap the next. Presumably some sort of controller level failure. My standard recommendation here is to consider then no more or less reliable than traditional disks and always put them in RAID-1 pairs. Two of the drives were Intel X25 models, the other was some terrible OCZ thing.
Out of more current drives, I was early to recommend Intel's 320 series as a cheap consumer solution reliable for database use. The majority of those I heard about failing died due to firmware bugs, typically destroying things during the rare (and therefore not well tested) unclean shutdown / recovery cases. The "Enterprise" drive built on the same platform after they tortured consumers with those bugs for a while is their 710 series, and I haven't seen one of those fail yet. That's not across a very large installation base nor for very long yet though.
The rationale behind splitting hard drives in a RAID between a number of manufacturers batches, even for identical drives, it to try and avoid a problem with an entire batch that's slipped past QA from taking out an entire array of drives simultaneously.
I'm paranoid, but am I paranoid enough....?
I have seen SSD death many times and it is a strange sight indeed. What is interesting about it when compared to normal drives is that when normal drives fail it is - mostly - and all or nothing ordeal. A bad spot on a drive is a bad spot on a drive. With SSDs you can have a bad spot one place, reboot, and you get a bad spot in another place. Windows loaded on an SSD will exhibit all kinds of bizarre behaviour. Sometimes it will hang, sometimes it will blue-screen, sometimes it will boot normally until it tries to read or write to that random bad spot. Rebooting is like rolling the dice to see what it will do next - that is, until it fails completely.
I have had two SSD crashes. One was on a very cheap Zelman 32GB drive which never really worked (OK, about twice). The other was on a Kingston 64GB that I have in my server. When it gets really hot in the room (over 100, so probably over 120 for the drive itself in the case), it will crash. But when it cools down, it works perfectly well.
Peter predicted that you would "deliberately forget" creation 2000 years ago...
SSD's have an advertised capacity N and an actual capacity M. Where M > N. In general the bigger M realtive to N the better the performance and lifetime of the drive. As it wears it will "silently" assign bad blocks and reduce M. Your write performance will degrade. If you have good analysis tools it will tell you when it starts getting a lot of blocks near end of life and when M is getting reduced.
Blocks near end of life are also more likely to get read errors. The drive firmware is supposed to juggle things around so all of the blocks near end of life about the same time. With a soft read error the block will be moved to a more reliable portion of the SSD. That means increased wear.
1. Watch write perforamance/spare block count
2. If you get any read errors do a block life audit
3. When you get into life limiting events things accelerate to bad due to the mitigation behaviors
Be carefull depending on the sensitivities of the firmware it will let you get closer to catastrophe before warning you. More likely to be closer in consumer grade.
With traditional mechanical drives, you usually get a clicking noise accompanied by a time period where you can offload data from the drive before it fails completely.
Usually? No.
This does happen sometimes, but it certainly doesn't happen "usually". There's enough different failure mechanisms for hard drives that there isn't any one "usual" method --
1- drive starts reporting read and/or write errors occasionally, but otherwise seems to keep working
2- drive just suddenly stops working completely all at once
3- drive starts making noise (and performance usually drops massively), but the drive still works.
4- drive seems to keep working, but smart data starts reporting all sorts of problems.
Personally, I've had #1 happen more often than anything else, usually with a healthy serving of #4 at about the same time or shortly before. #2 is the next most common failure mode, at least in my experience.
The sectors you are talking about are often referred to as "remaps" (or "spares"), which is also used to describe the number of blocks that have been remapped. Strategies vary, but an off-the-cuff average would be around one available spare per 1000 allocatable blocks. Some firmware will only use a spare from the same track, other firmware will pull the next nearest available spare. (allowing an entire track to go south)
The more blocks they reserve for spares, the lower the total capacity count they can list, so they don't tend to be too generous. Besides, if your drive is burning through its spares at any substantial rate, doubling the number of spares on the drive won't actually end up buying you much time, and certainly won't save any data.
But with the hundreds of failing disks I've dealt with, when more than ~5 blocks have gone bad, the drive is heading out the door fast. Remaps only hide the problem at that point. If your drive has a single block fail when trying to write, it will be remapped silently and you won't ever see the problem unless you check the remap counter in smart. If it gets an unreadable block on a read operation, you will probably see an io error however. Some drives will immediately remap it, but most don't and will conduct the remap when you next try to write to that cell. (otherwise they'd have to return fictitious data, like all zeros)
So I don't particularly like automatic silent remaps. I'd rather know whean the drive first looks at me funny so I can make sure my backups are current and get a replacement on order, and swap it out before it can even think about getting worse. I prefer to replace a drive on MY terms, on MY schedule, not when it croaks and triggers any grade of crisis. There are legitimate excuses for downtime, but a slowly failing drive shouldn't be one of them.
All that said, on multiple occasions I've tried to cleanse a drive of IO errors by doing a full zero-it format. All decent OBCCs on drives should verify all writes, so in theory this should purge the drive of all IO errors, provided all available spares have not already been used. The last time I did this on a 1TB Hitachi that had ONE bad block on it, it still had one bad block (via read verify) when the format was done. The write operation did not trigger a remap, (and I presume it wasn't verified, as the format didn't fail) and I don't understand that. If it were out of remaps, the odds of it being ONE short of what it needed is essentially zero. So I wonder in reality just how many drive manufacturers aren't even bothering with remapping bad blocks. All I can attribute this to is crappy product / firmware design.
I work for the Department of Redundancy Department.
I recently had a "old" (cir 2008) 64gb SSD drive die on me. It's death followed this pattern:
After popping a new disk in and doing a partition resize, my system was back up and running with no data loss. Of all the storage hardware failures I've experienced, this was probably the most pain-free as the failure caused the drive to simply degrade into a read-only device.
Karma: SELECT `karma` FROM `users` WHERE `userid`=138474;
I've seen two instances where a drive failed. Each time there were no handy replacement drives. Within a week a second drive died the same way as the first! back to backup tapes! Better to have replacement drives in boxes waiting.
This. Your spares closet is your best friend in the enterprise. Ensure you keep it stocked.
For those who are interested the white paper is titled "Failure Trends in a Large Disk Drive Population" and can be found here. It is a fairly short read (13 total pages) and quite interesting if you are into monitoring stuff.
Time to offend someone
I have ordered approximately 500 Intel SSD's over the past 18 months (320 series and the 520 series primarily). To date, we have had exactly one fail to my knowledge. It was a 320 series 160 GB with known firmware issue. We have around 80 of that type and size, and the drive that failed did so on first image. We RMA'ed the drive and got a replacement.