Re: Re-map disk sectors in userspace when rewriting after read errors

[Matthias Urlichs <matthias@urlichs.de>]

On Tue, 2009-09-15 at 21:14 +0300, Majed B. wrote:
> Hmm, so I guess I'm luckier since I run RAID5? (or not because I have
> 2 bad disks? :p)
> 
Well, depends on whether you have two errors in the same sector. If not,
you're going to be lucky.

> When do you expect to have a working application done, by the way?
> 
Hopefully later this week. It'll probably be a patch to mdadm's
development branch of some sort.

Neil: In order to do that, I need to read badblock map files for some
(or all) disks, in GNU dd_rescue's format preferably. Do you have a
preference WRT how to tell mdadm about these?

I tend towards "mdadm --recover 0:foo,2:bar DISK_DEVICE...". This would
tell mdadm that the badblock map for disk 0 is in file 'foo', the map
for disk 2 is in 'bar', and the other disks are supposed to be cleanly
read/writeable.

mdadm would then read RAID info from these devices, make sure it's
consistent (or "mostly consistent" if using --force), read the bad block
map, recover the data that's indicated to be bad and write it to the
partitions in question, and zero out the blocks that are unrecoverable
(and restore P+Q vectors for them).