Re: No response?

[Mark Bellon <mbellon@mvista.com>]

Gordon Henderson wrote:

>On Thu, 20 Jan 2005, David Dougall wrote:
>
>  
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>>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..
>
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>> I
>>thought software raid would mask all of this and just fail the drive.
>>    
>>
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>It should.
>
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>>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?
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Not that I know of but I would need to look. Any XFS wizard's comments?

mark

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>>If it makes a difference, I am running linux-2.4.26
>>    
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>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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