[Tfug] Drive recovery

[Tom Rini]

On Wed, Jun 03, 2009 at 02:55:19PM -0700, Bowie J. Poag wrote:

> dd is completely unaware of what a sector is -- It's completely agnostic  
> when it comes to input. The idea is, recover what can be  
> recovered--there's no point in obsessing over  the unreadable. Since  
> we're telling it to read off a block device, it becomes the  
> responsibility of whatever storage driver is handling the requests to  
> satisfy dd. All dd wants is "next, until there is no more "next" to  
> read. The resulting iso image might be sane enough to repair and then  
> have its contents dumped into a new filesystem.

IOW, dd might well hang, depending on just how unhappy the disk is at
this point in time and/or how the kernel responds to this unhappiness.

Personally (thankfully) when I've been roughly in this state, I've at
least been able to mount the disk and I rsync/copy to a new drive what I
can.

For the original email, does XFS not let you specify where to look FIRST
for superblock info/etc?  IIRC you can with ext[234] and that's how you
force one of the backups to be used.  Finally, it might, but XFS makes
this harder, be worth trying different OSes, again due to how different
OSes want to deal with unhappy filesystems.  For example I've had some
luck saving stuff off of dying HFS+ disks with Linux over OSX.

-- 
Tom Rini