Re: end to end error recovery musings

[Theodore Tso <tytso@mit.edu>]

On Fri, Feb 23, 2007 at 05:37:23PM -0700, Andreas Dilger wrote:
> > Probably the only sane thing to do is to remember the bad sectors and 
> > avoid attempting reading them; that would mean marking "automatic" 
> > versus "explicitly requested" requests to determine whether or not to 
> > filter them against a list of discovered bad blocks.
> 
> And clearing this list when the sector is overwritten, as it will almost
> certainly be relocated at the disk level.  For that matter, a huge win
> would be to have the MD RAID layer rewrite only the bad sector (in hopes
> of the disk relocating it) instead of failing the whiole disk.  Otherwise,
> a few read errors on different disks in a RAID set can take the whole
> system offline.  Apologies if this is already done in recent kernels...

And having a way of making this list available to both the filesystem
and to a userspace utility, so they can more easily deal with doing a
forced rewrite of the bad sector, after determining which file is
involved and perhaps doing something intelligent (up to and including
automatically requesting a backup system to fetch a backup version of
the file, and if it can be determined that the file shouldn't have
been changed since the last backup, automatically fixing up the
corrupted data block :-).

						- Ted