fsync() and disk flushes

fsync() and disk flushes

Posted Apr 2, 2009 23:28 UTC (Thu) by anton (guest, #25547)
In reply to: fsync() and disk flushes by iabervon
Parent article: That massive filesystem thread

And if you suddenly lose power, in his experience, the drive is actually much more likely to wipe out some arbitrary track of data from the disk than it is to have anything in the write cache and lose it.

While I have experienced drives that damage sectors or tracks on power loss, I consider these drives faulty; and with such drives the problem does not seem to be limited to drives that are trying to write something at the time. However, most drives don't wipe out arbitrary data in my experience.

But I have tested two drives with a test program for out-of-order writing, and found that they both wrote data several seconds out of order with a certain access sequence. If we don't see more frequent problems from this, that's probably because the disks don't optimize accesses as aggressively as some people imagine.

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