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Enterprise SSDs, Powered Off, Potentially Lose Data In a Week
New submitter Mal-2 writes with a selection from IB Times of special interest for anyone replacing hard disks with solid state drives:
The standards body for the microelectronics industry has found that Solid State Drives (SSD) can start to lose their data and become corrupted if they are left without power for as little as a week. ... According to a recent presentation (PDF) by Seagate's Alvin Cox, who is also chairman of the Joint Electron Device Engineering Council (JEDEC), the period of time that data will be retained on an SSD is halved for every 5 degrees Celsius (9 degrees Fahrenheit) rise in temperature in the area where the SSD is stored. If you have switched to SSD for either personal or business use, do you follow the recommendation here that spinning-disk media be used as backup as well?
If the contents are lost in a week, we're probably talking about capacitor-backed SSDs that use some other technology than flash memory. Yes, it would be insane to use flash memory for archival purposes as well, but it still should easily retain its contents for at least a decade. When powered on, this problem does not exist as normally the controller slowly walks through the flash refreshing it.
Data loss in flash cells is probabilisitic, but the standard for wear levelling software is to mark a cell as dead if it can't guarantee holding its contents for a year. There have been some interesting proposals to expose this to the OS - there's a lot of data where even holding it for one day would be fine (e.g. browser caches, swap, other temporary files), so the more worn cells could be productively used for this data.
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The relevant table is on 27. page.
In short: if you use the SSD in a cold environment AND store it in hot environment than you may lose data quite quickly. Quicker than two weeks.
Client drives are also affected, but the data loss occurs slighly later. I guess reason of the difference is that enerprise drives assume a higher work temperature.
So the advice is that if you use the SSD in your air conditioned basement in a good case then do not store your SSD on the sun for extended periods.
And no, I do not use spinning media as a backup. I use tapes. Using spinning media for proper backups is almost impossible. See http://www.taobackup.com/
When ever something is "Enterprise" class it means it is vastly inferior to other solutions on the market but cost 3x as much.
For some reason this isn't a buzzword that sends shivers down every IT workers spine yet.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
You may be right in case of other equipment, but enterprise grade drives are really better. For example I do not know any consumer SSD which has power loss capacitors (Intel 320 is not produced anymore). Most consumer drives don't contain even those capacitors which would be necessary to prevent the loss of - not the freshly written but the - old(!) data in case of a power loss. Consumer HDDs lied (or lying?) about sync, they confirm sync before they actually save the data to disk. And I am sure that consumer SSDs do something similar, because consumer SSD are usually faster (although their speed frequently fluctuates to extreme extents) than their corresponding enterprise variants, which is impossible in a safe way without power loss protection capacitors.
FTFS:
If you have switched to SSD for either personal or business use, do you follow the recommendation here that spinning-disk media be used as backup as well?
So how do backups help you? Except for ZFS and btrfs (?), no file systems check for data integrity. You're not going to detect the bitrot taking place, and you'll happily send that rotten data to your backup until the corruption is noticed in some other way.
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To the people saying 'no datacenter goes without power for a week'. I know one that did due to a natural disaster. THey spent 1000's of hours bringing that datacenter up. Do you think they would have wanted to have been messing around reconfiguring raid arrays and rebuilding on top of that? It is not just the data you lose, it is the configuration.
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Your stuff's cargo container was not heated during shipping. If it was stacked below the deck line, where it was not exposed to the sun, it didn't reach 55C during the journey.
John
If the temperature in my pockets exceeds 55C, then data on a flash drive is not likely to be my biggest concern. YMMV.
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Haha! I'm old enough to remember when Seagate was the best.
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reason being that you shouldn't be buying Enterprise grade through a brick retailer. You should be leasing it via a support contract: the premium is with a tech on the other end of the phone who's out in a couple hours to replace a dud drive and have your RAID rebuilt before the day ends, rather than you running to the nearest PC World for a TB Seagate pocket spinny. Like I've just had to. If I'd had a support contract (hence Enterprise grade drives as they generally insist on anyway since they're easier for ICTs to RMA) then I'd've been at my mum's now sealing her windows rather than babysitting my new drive still.
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I skimmed though Seagate's paper. At first glance, it appears to have a hidden agenda. That is to make hard drives preferable to solid state drives for everyday use, as Seagate primarily sells hard drives. For long term storage that is what is generally done anyway due to cost, along with tape. For performance, 120+ GB SSD's cannot be beaten, one on one, by any hard drive. Does anyone know of data that indicates that (non-OCZ) drives lose data over time during use, not when powered off for many months after use? Seagate's paper may not be useful if it doesn't correspond to real world use.
If you have switched to SSD for either personal or business use, do you follow the recommendation here that spinning-disk media be used as backup as well?
First, anything stored on any kind of drive should be backed up if you care about it.
Second, if you do backup, who backs up to SSD? You don't need frequent fast random-access on backups, and SSD is about the most expensive storage technology around per-GB. Anybody doing bulk storage is going to be doing it on either hard disks, tape, or something optical.
So, if you're backing your data up, you'll be backing it up to something safe most likely.
Of course, this does bring up the need for the ability to verify the integrity of your data at-rest, and right now I'd say ZFS/btrfs are the best way of accomplishing this. You could also do hashing above the filesystem layer, but that requires a lot of overhead if your files change frequently. If your files don't change much than something like tripwire would be fine. You'd want to run that more often than you rotate your backup media so that you don't discard the last-known-good version of anything.
Yes, conceptually all flash data has to decay when powered off. But implementation tradeoffs vary widely. A dirt-cheap Microchip PIC18F2580 microcontroller has flash data retention without refresh "conservatively estimated" at 40 YEARS MINIMUM and 100 years typical (page 3, 10, 435). The number of previous erase/program cycles that retention is predicated on is not given, but is probably a single one, or a few, out of a typical endurance of 100,000 cycles and a minimum of 10,000 from -40 to +85 C. AFAIK there is no wear leveling or block sparing in microcontroller flash memories.
I have NEVER HEARD of an embedded guy ever running into a case of either cycle exhaustion or data decay in the program memory such microcontrollers (if data is written to flash during operation, specs do have to be considered).
SSDs have flash design tradeoffs remarkably different from this. For example, MLC individual cell endurance is around 1000-10,000, and retention is far less as seen in the article and comments here. In return, the access time is vastly faster and the density vastly higher.
Tape is some of a myth.
The only safe media, is that which you keep copying before it deteriorates. Not HDDs, not SSDs, not CDs, not thumbdrives, and not tape. Any media you leave untouched past its data retention period, will lose data.
What you need is to check every copy of your data for any sign of degradation, and replace it with a fresh copy as soon as, or before, it begins to fail. Tape may give you the most time between checks, but it doesn't change the fact that data you forget about is data you will lose.
You should be leasing it via a support contract: the premium is with a tech on the other end of the phone who's out in a couple hours to replace a dud drive and have your RAID rebuilt before the day ends
I always think the idea of giving back a storage device that has had real data on it under some long-term warranty or rapid on-site service agreement is mostly marketing spin.
Every company I work with has a simple policy on this, for basic security/privacy reasons: a drive that is DOA can go back, but anything that has ever been touched by real data is written off and securely destroyed. Any warranty longer than a few days is therefore worthless to us, as is any rapid service support contract if all it's going to do is swap the failed drive out for a new one.
Obviously this is only applicable to drives where recovering data is potentially possible. If everything (including things like swap space) was encrypted before it hit the drive's controller then returning the unit is in theory an option. But usually it's not worth the trouble to verify that this was the case throughout whatever working life any drive had, and permanent encryption introduces a significant performance hit.
I've seen enterprise support contracts from major brands that specifically say a failed drive won't have to be returned for exactly these reasons.
If you disagree, post your argument. (-1, Overrated) isn't your personal censorship tool for views you don't like.
Newer 3D NAND is using a charge trap design which basically solves the electron leakage issue found with the older floating gate NAND...
Also, the move to the newer 3D NAND brings us back up to 40nm processes vs the 10nm gates we are currently working with, allowing for much better reliability.
Disclaimer: I've been selling enterprise flash storage for the last 6 years.
up 12 days, 22:30, 2 users, load averages: 993.20, 994.21, 994.56
*makes note to limit user processes...
Read again - more temperature means less time. So if there's no lower limit, SSD without power will be best stored at 0 Kelvin
No I read the article. It's related to electron mobility at the time the data is written. If you heat up the SSD after it's turned off, electron mobility increases and you'll get more leakage. But if you wrote data when it was hot, you have a better signal to noise ratio.