Three comments

Posted Jul 14, 2006 19:30 UTC (Fri) by ncm (guest, #165)
In reply to: Three comments by nix
Parent article: Crash-only software: More than meets the eye

I don't know to what degree modern drives really obey write barriers. If history is any guide, they obey write barriers when the data rate is low, but toss them when the buffers fill up, or any time they seem to recognize a benchmark being run. In any case, they won't protect against sectors being half-written.

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Three comments

Posted Jul 18, 2006 6:21 UTC (Tue) by nix (subscriber, #2304) [Link] (1 responses)

That's just horrible enough that it might be true, but the idealist in me hopes that it isn't, because it would render the entire concept of write barriers pointless :(

Three comments

Posted Jul 18, 2006 9:04 UTC (Tue) by ncm (guest, #165) [Link]

Not at all... it just means that backup power is necessary for a reliable system. Disk drive designers have learned not to pretend they can make a whole system reliable all by themselves, and that (furthermore) the market won't pay for them to try. It doesn't take much backup power; if you can get the CPU's or ATA interface's power to drop out of tolerance a few seconds before the drive's, that may be all you need.