fsync() and disk flushes [LWN.net]

fsync() and disk flushes

Posted Apr 3, 2009 0:02 UTC (Fri) by nix (subscriber, #2304)
In reply to: fsync() and disk flushes by xoddam
Parent article: That massive filesystem thread

RAID doesn't really solve sudden-power-loss situations: in fact RAID-5 in
particular can make it much worse (turning small-range corruption into
apparent scattershot corruption).

A UPS, or battery-backing, is the answer (well, moves the failure point:
if it's a UPS, the UPS must fail before you lose: if it's battery-backed,
you often have to lose the battery first, then power, which is likely to
happen because you often have no idea the battery has failed until it's
too late).

In conclusion: we all suck, our data is doomed, the Second Law shall
triumph and Sod and Murphy shall dance above our mangled filesystems.

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fsync() and disk flushes

Posted Apr 4, 2009 0:01 UTC (Sat) by giraffedata (subscriber, #1954) [Link]

The answer is RAID and UPS, but not that way. The RAID goes over the UPS; e.g. a mirror of two disk drives, each with its own UPS.

Such redundancy also makes it possible to test the UPS regularly and avoid the problem of two dead batteries when the external power fails.

The UPS doesn't count if you don't test, measure, and/or replace the its battery regularly.