kern/85603: [ata] FS corruption and 'uncorrectable' DMA errors
on ATA disks after unclean shutdown
Søren Schmidt
sos at deepcore.dk
Wed Jan 4 13:30:49 PST 2006
The following reply was made to PR kern/85603; it has been noted by GNATS.
From: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos at deepcore.dk>
To: bug-followup at FreeBSD.org, philip at FreeBSD.org
Cc:
Subject: Re: kern/85603: [ata] FS corruption and 'uncorrectable' DMA errors
on ATA disks after unclean shutdown
Date: Wed, 04 Jan 2006 20:24:17 +0100
Uncorrectable errors can very easily be encountered if there was a write
operation on a drive during a power failure. The problem is that the
sector(s) isn't completely written and the ECC information isn't updated
correctly on the media. This can render from 1 sector to an entire track
(seen from the disks perspective not nessesarily the geometry used) due
to the way data are stored on modern disks.
Now, if the disk still has spare sectors available a write to the bad
sectors will be remapped and the disk will seem to be functional again.
I have seen at least a dozen modern systems that actually powercycles
during reset, which can be a very bad idea if the drives have decided to
write out cachebuffers etc during a reboot.
-Søren
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