QMail and SoftUpdates

Mikhail Teterin mi+mx at aldan.algebra.com
Thu May 20 13:16:25 PDT 2004


=> Even if the OS crashes, as long as power is supplied to the drive,
=> its firmware should finish writing the data from its cache to the
=> disk media, no? And therefore, as long as one has a stable power
=> source, e.g. running off a UPS, there really isn't any great risk
=> from on-drive write caches, is there?
=
=No. Unlike SCSI disks, ATA disks will toss their write-cache on a
=reset. When the system crashes and the BIOS starts rebooting, guess
=what it issues to the ATA disks? Yep, a reset. So with ATA write-cache
=enabled, your filesystem is likely to be toast after a crash, as well
=as after a power failure.

Is not this only of concern if the power is restored and the BIOS resets
the disks _before_ they flush their write caches? I'd expect them to do
that (the flushing) within seconds anyway, no?

	-mi



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