Messages in this thread | | | Date | Thu, 30 Oct 2003 08:30:37 GMT | From | John Bradford <> | Subject | Re: Blockbusting news, results get worse |
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Quote from Pavel Machek <pavel@ucw.cz>: > Hi! > > > > >> or put it under heavy write workload and remove > > > >> power. > > > >> > > > > Can you tell us more about what really happens to disk drives when the > > > > power is cut while a block is being written? We engage in a lot of > > > > uninformed speculation, and it would be nice if someone who really knows > > > > told us.... > > > > > > > > Do drives have enough capacitance under normal conditions to finish > > > > writing the block? Does ECC on the drive detect that the block was bad > > > > and so we don't need to detect it in the FS? > > > > > > > > > Does it really matter to speculate about this? > > > > > > If you don't FLUSH CACHE, you have no guarantees your data is on the > > > platter. > > > > I think that the idea that is floating around is to deliberately ruin > > the formatting on part of the drive in order to simulate a bad block. > > > > Operation of disk drives immediately after a power failiure has been > > discussed before, by the way: > > > > http://marc.theaimsgroup.com/?l=linux-kernel&m=100665153518652&w=2 > > Well, that looks like pure speculation. > > BTW I *do* believe that powerfail can make the sector bad. Imagine you > bump into bad sector during write, and need to reallocate...
See the rest of the thread.
I think the point is that if that happened, it would be outside the scope of the solution being suggested, and something more elaborate such as a battery backed cache is needed if you want to guard against that situation.
Unfortunately, I think that the re-writing due to a bad sector requirement is going to occur often enough to make any solution which doesn't handle it a bit pointless :-(
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