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SubjectRe: Journaling pointless with today's hard disks?
Chris Wedgwood (cw@f00f.org) wrote :

> On Sat, Nov 24, 2001 at 02:03:11PM +0100, Florian Weimer wrote:
>
> When the drive is powered down during a write operation, the
> sector which was being written has got an incorrect checksum
> stored on disk. So far, so good---but if the sector is read
> later, the drive returns a *permanent*, *hard* error, which can
> only be removed by a low-level format (IBM provides a tool for
> it). The drive does not automatically map out such sectors.
>
> AVOID SUCH DRIVES... I have both Seagate and IBM SCSI drives which a
> are hot-swappable in a test machine that I used for testing various
> journalling filesystems a while back for reliability.
>
> Some (many) of those tests involved removed the disk during writes
> (literally) and checking the results afterwards.

What do you mean by "removed the disk" ?

- rm /dev/hda ? :-)
- disconnect the disk from the SCSI or ATA bus ?
- from the power supply ?
- both ?
- something else ?

>
> The drives were set not to write-cache (they don't by default, but all
> my IDE drives do, so maybe this is a SCSI thing?)
>
> At no point did I ever see a partial write or corrupted sector; nor
> have I seen any appear in the grown table, so as best as I can tell
> even under removal with sustain writes there are SOME DRIVES WHERE
> THIS ISN'T A PROBLEM.
>
> Now, since EMC, NetApp, Sun, HP, Compaq, etc. all have products which
> presumable depend on this behavior, I don't think it's going to go
> away, it perhaps will just become important to know which drives are
> brain-damaged and list them so people can avoid them.
>
> As this will affect the Windows world too consumer pressure will
> hopefully rectify this problem.
>
> --cw
>
> P.S. Write-caching in hard-drives is insanely dangerous for
> journalling filesystems and can result in all sorts of nasties.
> I recommend people turn this off in their init scripts (perhaps I
> will send a patch for the kernel to do this on boot, I just
> wonder if it will eat some drives).

--
David Balazic
--------------
"Be excellent to each other." - Bill S. Preston, Esq., & "Ted" Theodore Logan
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