Re: ide write cache issue? [Re: Something corrupts raid5 disks slightly during reboot]

From: Ville Herva
Date: Sat Nov 01 2003 - 16:03:08 EST

On Sat, Nov 01, 2003 at 08:01:14PM +0100, you [Willy Tarreau] wrote:
> On Sat, Nov 01, 2003 at 08:25:18PM +0200, Ville Herva wrote:
> > Is there anything special in booting to DOS instead of different linux
> > kernel, other than that it would rule out some strange kernel bug that is
> > present in 2.2 and 2.4?
> No, it was just to quicky confirm or deny the fact that it's the kernel
> which causes the problem. It could have been a long standing bug in the IDE
> or partition code, and which is present in several kernels.

I vaguely recall some ide write cache flushing code was fixed some time ago,
but I can't find it in the archives. Maybe I dreamed that up. But I still
wonder why an otherwise idle drive would hold the data in write cache for so
long (several minutes.)

> But as you say that it affects two different controllers, there's little
> chance that it's caused by anything except linux itself.

Unless the drive is buggy wrt. flushing its write cache. But I think it's
a quite distant possibility.

> Then, the reboot on DOS will only tell you if the drives were corrupted at
> startup or at shutdown.

Yep. I'll try to find the moment to boot the beast into something else than
the current kernel / distro (it could in theory be something in userspace,
though I cannot think what).

> > BTW: the corruption happens on warm reboots (running reboot command), not
> > just on power off / on.
> OK, but the BIOS scans your disks even during warm reboots.

True, I mainly made this note because I hadn't mentioned it before in the
thread, and I thought it might have some relevance wrt. possible ide write
caching problems. I didn't mean it as a response to the BIOS theory.

-- v --

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