Re: Driver retries disk errors.

[Theodore Ts'o <tytso@mit.edu>]

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