how does ext3 handle no communication to storage

[Sev Binello]

Hi -
    We had the conversation below a while back.
    I was wondering if a patch was ever put together to address this issue

Thanks
-Sev



-- 

Sev Binello
Brookhaven National Laboratory
Upton, New York
631-344-5647
sev at bnl.gov




Theodore Tso wrote:
> On Mon, Aug 28, 2006 at 03:04:26PM -0400, Sev Binello wrote:
>   
>> Can anyone tell us what the expected behavior is,
>> in the event that ext3 loses total contact with the storage system ?
>>
>> We have found that the file system is put into read only mode,
>> it is then found to contain errors, and requires an fsck.
>> Sometimes the fsck finds numerous (some serious looking) errors,
>> and that running without fsck doesn't seem like a safe option.
>>
>> We are trying to understand why exactly this is.
>> Why do we get errors ?  Why serious ones ?
>>
>>     
>
> The filesystem should go read-only when you try to modify it.
> HOWEVER, the problem comes when connectivity is restored.  When an
> attempt to modify the filesystem fails, the journal is aborted and an
> I/O is returned.  However, there may be modified blocks left hanging
> about in the buffer cache before the kernel realized that connectivity
> has been lost, and what we need to do is to make sure that all dirty
> blocks in the buffer cache and page cache are dropped.
>
> Basically, if I'm right, this is a bug, which we need to fix.  That
> patch would require flushing all modified buffers and page cache pages
> when the filesystem goes read-only.  The modified buffers is the more
> important thing, since that's what causes the filesystem corruption,
> although for correctness's sake we should be flushing any modified
> page cache pages as well.  I don't have time to code this right now,
> but I'll try to get a patch out to relatively soonish, if you're
> willing to try it to see if it addresses your observed problem.
>
> 						- Ted
>
>