How Power Failures Corrupt Flash SSD Data 204
An anonymous reader writes "Flash SSDs are non-volatile, right? So how could power failures screw with your data? Several ways, according to a ZDNet post that summarizes a paper (PDF) presented at last month's FAST 13 conference. Researchers from Ohio State and HP Labs researchers tested 15 SSDs using an automated power fault injection testbed and found that 13 lost data. 'Bit corruption hit 3 devices; 3 had shorn writes; 8 had serializability errors; one device lost 1/3 of its data; and 1 SSD bricked. The low-end hard drive had some unserializable writes, while the high-end drive had no power fault failures. The 2 SSDs that had no failures? Both were MLC 2012 model years with a mid-range ($1.17/GB) price.'"
We encountered something like this (Score:5, Interesting)
We encountered extensive and progresssive file corruption on SSDs in an industrial device. It used the FAT file system, and after every loss of power, it ran its equivalent of chkdsk/f at the next boot. If power was lost again while this command was running, then it was guaranteed that the file system would become corrupt (despite the fact that we were writing nothing to the SSD; it held only files which were opened for reading). The window of opportunity was described as "very short", and the possibility of corruption was "very small" according to the vendor. In our experience in the field, and in our internal testing, the window of opportunity exceeded 20 seconds, and the possibility of corruption was "utter certainty".
The vendor fixed the problem in a very easy way. They changed the file system from FAT to a commercial journaling FS. In our subsequent tests, we never found any file corruption, even on iterated power loss at random intervals after power on.
Re:We encountered something like this (Score:4, Interesting)
I hate a lot of USB drives and CompactFlash. They're all designed as dumb commodity devices for the undiscriminating user, and trying to get any solid spec sheets out of the manufacturers is impossible if you're not also a giant corporation. Instead their data sheets are just marketing literature (you rarely get anything more technical than "8x speed"). Almost all are designed to work with Windows with no concern to work with embedded systems or production automation, etc. So you end up buying a wide variety to test with and see which ones are barely adequate to work with your system.
Re:We encountered something like this (Score:5, Interesting)
Not just a lot of them, most of them, to the point that my former contract rolled their own due to flaky controllers, etc put out by the SSD manufacturers. Yes, they found it cheaper and more efficient to make their own SSD drives, and to incinerate the ones that failed in a blast furnace than rely on the crap the manufacturers are currently foisting on the market.
Re:We encountered something like this (Score:5, Interesting)
You might check into adding supercaps into the power supply, across the DC output lines.
For a less DY method, you could try this: http://www.beam-tech.com/093001/prd_pgs/internal_ups.htm# [beam-tech.com]
It's an internally mounted, UPS. There are also some PC power supplies that have the UPS built-in, but expect to pay a premium for those.
If your application allows it, you might want to just mount your SSD into a laptop. It already has internal battery power, and there isn't any exotic hardware you have to pay through the nose for.