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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?
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/
The statements are actually completely accurate, but a bit misleading. First, this is about what JEDEC requires, not what actual SSDs deliver. Second, this is when SSDs are stored in idle at 55C. And third the JEDEC requirements for minimum off-time data-retention are only 3 months @40C for enterprise-grade SSDs and only 12 months for consumer SSDs at 30C. These are kind of on the low side, although I have lost some OCZ drives that were off for just about a year. (Never buying their trash again...)
That said, anybody conversant with SSD technology knows that SSDs are unsuitable for offline data storage as data obviously has potentially far shorter lifetimes than on magnetic disks, which in turn again have far shorter data lifetime than archival-grade tape. These is absolutely no surprise here for anybody that bothered to find out what the facts are. Of course, there are always those that expect every storage tech to keep data forever, and those dumb enough to have no or unverified backups and those often on media not suitable for long-term storage. Ignoring reality comes at a price.
My personal solution is mixed HDD/SSD Raid1 and, of course, regular backups.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
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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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
Every write, not every read. Reads are satisfied as soon as either drive returns the data. And if the raid controller has a battery or supercap so it can cache writes, you'll almost never notice the difference.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
I might be wrong but isn't it also when the SSD is stored at 55C AFTER having been stress tested at 55C to their endurance rating in terabytes written (page 39) under a given workload?
And even then the cherry picked value was in example data submitted by Intel for unknown hardware and very likely extrapolated and quite possibly meaningless because it wasn't part of the chart targeted for the standard.
The article seems to have totally misrepresented the presentation's purpose: which is to lay out endurance testing methodology/standards.
The only important values were on page 26 where they set the minimum requirements of 40C 8hr/day load/30C 1 year retention for consumer (with a higher error ratio) and 55C 24hr/day load/40C 3 months retention for enterprise (with a lower error ratio.)
And it looks like they haven't actually worked out the consumer workload for testing yet.
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.
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.
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