Gordon Henderson wrote:
On Thu, 20 Jan 2005, David Dougall wrote:
Perhaps I was asking a stupid question or an obvious one, but I have received not response. Maybe if I simplify the question...
If I am running software raid1 and a disk device starts throwing I/O
errors, Is the filesystem supposed to see any indication of this?
No..
I
thought software raid would mask all of this and just fail the drive.
It should.
I have servers with xfs as the filesystem and xfs will start to throw I/O
errors when a disk starts acting up even with software raid in between.
Please advise on how I can confirm my setup or if this is possibly a bug
how to diagnose further.
I've experienced long delays (30 seconds? It seemed longer) in a system
when a disk fails for a genuine reason - (I've deliberately run badblocks
on an md device when I knew one of the underlying devices had genuine bad
blocks) maybe the md code really tries hard to read the block, maybe the
underlying device driver tries really hard), but in these cases, I've seen
the system more or less freeze (all processes accessing that device
anyway) until the raid code decided to kick the device out of the array.
I've seen this too. The worst case can actually last for over 2 minutes.
We've been running with a patch to the RAID 1 driver that handles this so critical applications do not hang for too long. Basically it uses timers in the RAID 1 driver to force the disk to be treated as actually having failed if it doesn't respond within a reasonable time (tunable but usually ~3 seconds). It then handles the I/O requests coming back async. and does the clean up.
Maybe XFS has a timer and doesn't like devices to "go away" for a long period of time?
Not that I know of but I would need to look. Any XFS wizard's comments?
mark
If it makes a difference, I am running linux-2.4.26
I've used 2.4.x for a long time - I did try xfs about a year ago, but wasn't happy with it all (for various reasons).
Gordon
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