Re: Driver retries disk errors.

[James Courtier-Dutton <James@superbug.demon.co.uk>]

Theodore Ts'o wrote:
> On Mon, Aug 30, 2004 at 06:39:31PM +0200, Rogier Wolff wrote:
> 
>>We encounter "bad" drives with quite a lot more regularity than other
>>people (look at the Email address). We're however, wondering why the
>>IDE code still retries a bad block 8 times? 
> 
> 
> I could see retrying 2 or 3 times, but 8 times does seem to be a bit
> much, agreed.
> 
> 
>>In fact we regularly are able to recover data from drives: we have a
>>userspace application that retries over and over again, and this
>>sometimes recovers "marginal" blocks. This could be considered "good
>>practise" if there is a filesystem requesting the block. On the other
>>hand, when this happens, the drive is usually beyond being usable for
>>a filesystem: if we recover one block this way, the next block will be
>>errorred and the filesystem "crashes" anyway. In fact this behaviour
>>may masquerade the first warnings that something is going wrong....
> 
> 
> If the block gets successfully read after 2 or 3 tries, it might be a
> good idea for the kernel to automatically do a forced rewrite of the
> block, which should cause the disk to do its own disk block
> sparing/reassignment.  
> 
> 						- Ted

It does the same retries with CD-ROM and DVDs, and if the retries fail, 
it disables DMA! It even does the retries when reading CD-Audio.
Maybe there should be a "retrys" setting that can be set by hdparm, then 
we could set the retry counts, and what happens when a retry fails on a 
per device basis.