On Sun, 2017-05-07 at 22:40 +0200, Pavel Machek wrote: > > > NOTE: unclean SSD power-offs are dangerous and may brick the device in > > > the worst case, or otherwise harm it (reduce longevity, damage flash > > > blocks). It is also not impossible to get data corruption. > > > I get that the incrementing counters might not be pretty but I'm a bit > > skeptical about this being an actual issue. Because if that were > > true, the device would be bricking itself from any sort of power > > losses be that an actual power loss, battery rundown or hard power off > > after crash. > > And that's exactly what users see. If you do enough power fails on a > SSD, you usually brick it, some die sooner than others. There was some > test results published, some are here > http://lkcl.net/reports/ssd_analysis.html, I believe I seen some > others too. > > It is very hard for a NAND to work reliably in face of power > failures. In fact, not even Linux MTD + UBIFS works well in that > regards. See > http://www.linux-mtd.infradead.org/faq/ubi.html. (Unfortunately, its > down now?!). If we can't get it right, do you believe SSD manufactures > do? > > [Issue is, if you powerdown during erase, you get "weakly erased" > page, which will contain expected 0xff's, but you'll get bitflips > there quickly. Similar issue exists for writes. It is solveable in > software, just hard and slow... and we don't do it.] It's not that hard. We certainly do it in JFFS2. I was fairly sure that it was also part of the design considerations for UBI — it really ought to be right there too. I'm less sure about UBIFS but I would have expected it to be OK. SSDs however are often crap; power fail those at your peril. And of course there's nothing you can do when they do fail, whereas we accept patches for things which are implemented in Linux.
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