Am 08.02.2016 um 21:31 schrieb f-dm-c@xxxxxxxxxxxxx:
> Date: Mon, 8 Feb 2016 17:41:43 +0100
> From: Arno Wagner <arno@xxxxxxxxxxx>
> The thing is that in a typical PC, power drops relatively
> slowly and disks work non-seeking for a lower voltage
> that the thresholds. Add to that that a single sector
> write takes less than 1ms (probably much less), and
> you get ample time to finish a write in progress.
If the data has already made it all the way into the drive itself,
that may be valid, but it's very dangerous to make such assumptions
in general, and you can't necessarily know the timing of the power
failure vs when the data makes it to the disk, much less the platters.
If the data hasn't made it to the drive (or rather is not in transit)
then the change is just discarded leaving us in a stable state.
http://zork.net/~nick/mail/why-reiserfs-is-teh-sukc
And new technologies may change this---not just SSDs, but modern
high-capacity drives that must rewrite many, many sectors to write
one. (Yes, I know this also argues that those headers should be
far away from each other. So be it. If such scattered headers
don't prevent resizing, I don't care. Except maybe for secure wipe.)
Well, if we talk about SMR, small changes will be written to the random
IO section of the drive and merged later. With those drives you'll
probably never know if there's parts of the old header lingering around
someplace else.
Regards
-Sven
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