A few days ago I came across an article on Datacenter Knowledge that was talking about Flash reliability. As much as I’d love to think that just because it’s solid state that it will last much longer, real world tests to-date haven’t shown that to be true in many cases.
I happened to have the manual open on my computer for the Seagate Pulsar SSD, and just saw something that was really interesting to me, on page 15 it says –
As NAND Flash devices age with use, the capability of the media to retain a programmed value begins to deteriorate. This deterioration is affected by the number of times a particular memory cell is programmed and subsequently erased. When a device is new, it has a powered off data retention capability of up to ten years. With use the retention capability of the device is reduced. Temperature also has an effect on how long a Flash component can retain its pro-grammed value with power removed. At high temperature the retention capabilities of the device are reduced. Data retention is not an issue with power applied to the SSD. The SSD drive contains firmware and hardware features that can monitor and refresh memory cells when power is applied.
I am of course not an expert in this kind of stuff, so was operating under the assumption that if the data is written then it’s written and won’t get “lost” if it is turned off for an extended period of time.
Seagate rates their Pulsar to retain data for up to one year without power at a temperature of 25 C (77 F).
Compare to what tape can do. 15-30 years of data retention.
Not that I think that SSD is a cost effective method to do backups!
I don’t know what other manufacturers can do, I’m not picking on Seagate, but found the data tidbit really interesting.
(I originally had the manual open to try to find reliability/warranty specs on the drive to illustrate that many SSDs are not expected to last multiple decades as the original article suggested).
This is specially relevant for digital photography. SD cards have fallen in price to the point where a surprisingly large number of people treat them like film, using them once until filled, and then switching to another card and storing the previous one as a backup. Clearly, this strategy will need revising.
Comment by Fazal Majid — February 19, 2011 @ 7:06 pm
Anyone else had to “cook” tapes in an autoclave?*
But i’m a fan of tape. Just not funny backup formats, which have stung before. Look at Zmanda or a better idea.
My thinking about SSD is that it already does so much error correction (MLC e.g. which is going “enterprise” but way quicker than PMR) to actually *work* that you cannot add another layer without pain. Ayone know of a controller which can talk to this?
At least the building where i work happens to be a natural spread spectrum Faraday cage, so i’m less concerned with quantum bit flipping 🙂
Fazal,
You have a proper point there.
I grew up in a photographic culture (my Uncle did this for war efforts) and regards digital, I’ve had some of the best kit ever. So i bought always the best cards i could.
But i was beaten out by a buddy who simply rode the curve and bought cards and treated them as write once devices. Him: no data loss. Me: occasional disastrous FAT formatting problems. (ha ha, the tax!) Because i had to reuse my very expensive cards. This is why any decent camera offers RAID1 on two cards in two slots.
Doesn’t make better pictures though!
* This is a very obscure reference, but you’d like the music, and if not that, the filming. In ’78-79 Joseph Losey filmed the opera “Don Giovanni” with the best cast ever. Gaumont, the film house, spent a indescribable amount of time getting it remastered. Biggest initial problem: cooking tapes to get them working. That actually failed, and they fluked out finding a copy in Sony’s dungeon storage of 80 miles of shelf (somewhere in New Jersey) which was not indexed and no-one had a clue.
So, if you store tapes, get good aircon. Unlike with server farms, you must drop the humidity and kill airflow velocities. My dearly missed and long lost to God, business partner was in that business too. But check out the darned movie, new edition, with the documentaries on them getting it back, it’s outrageously good!
cheers,
– john
Comment by John (other John) — February 23, 2011 @ 9:23 am
Hi, Nate. The ridiculously-remotely-good-news is that I saw one of the academic papers presented at FAST’11 this month was about how difficult it is to thoroughly/properly erase those SSD’s (http://www.usenix.org/events/fast11/tech/full_papers/Wei.pdf).
No, I didn’t actually read the whole thing; it’s quite a snoozer. Woody Leonhard at InfoWorld, though, had to read it in order to write this human-readable article: http://www.infoworld.com/print/152263
I don’t know how long their study took, but I don’t think bit-decay played a part. Looks like inactivity is a greater threat to data on SSD’s than intentional destruction, odd as that may be!
Comment by Charlie (PDX) — February 24, 2011 @ 10:44 am