mirror handling of broken harddrives

[Simon L. Nielsen]

On 2004.11.29 14:35:21 +0100, Terje Elde wrote:
> On Mon, Nov 29, 2004 at 12:57:17PM +0100, Simon L. Nielsen wrote:

> > ad0: TIMEOUT - WRITE_DMA retrying (2 retries left) LBA=152911
> > ad0: FAILURE - WRITE_DMA timed out
> > GEOM_MIRROR: Request failed (error=5). ad0[WRITE(offset=78290432, length=16384)]
> > GEOM_MIRROR: Device boot: provider ad0 disconnected.
> > GEOM_MIRROR: Device boot: provider ad0 detected.
> > GEOM_MIRROR: Device boot: rebuilding provider ad0.
> > GEOM_MIRROR: Device boot: rebuilding provider ad0 finished.
> > GEOM_MIRROR: Device boot: provider ad0 activated.
> >
> > So, it just works :-).
>
> Hmm, yes.  But does it work the way it should?
>
> I mean, if the reason for the problem is that the hardware ad0 is defect, then
> you'll try to rebuild it again and again.  Every time you're trying to write a
> defect sector, the disk will block.

That has not been the case for me.  The system has run without
problems for a couple of months with those rebuilds.  It's two old
10GB IBM disks which are only used for the root file system (since my
SATA and RAID controllers conflict so I can't boot from them).

Since newer ATA drivers has remapping of bad sectors, if there really
is a problem with a bad sector that cause an error, rebuilding the
array should cause the bad sector to be remapped.

It should also be noted that two SATA disks in the same system running
another mirror has not had any of those self rebuilds.

> Since this is a DMA timeout, I imagine the blocking can quite easily lead to
> other problems as well, for things sharing the same DMA channel.

I don't really think the timeout is related to DMA, just the disk not
responding for whatever reason (could be it's doing thermal
recalibration).  The disks are too old to have proper SMART support so
I can see if there are actual errors.

-- 
Simon L. Nielsen
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