Messages in this thread |  | | Date | Sun, 25 Nov 2001 22:14:18 +1300 | From | Chris Wedgwood <> | Subject | Re: Journaling pointless with today's hard disks? |
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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.
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). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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