Re: [Bug-ddrescue] Selective recovery

[Robert Trevellyan]

I'd pick the first option (clone the failing disk.) Assuming the areas of
the disk that identify it as a member of a RAID can be copied, I would
expect the system to accept a clone.

If you pick the second option, ddrescue will probably work (it just reads
from a file), but there will be more layers between ddrescue and the
failing disk, which could limit how much data ddrescue can recover.

Don't forget, you need a clone of the failing disk, then a copy of the
clone to work with. That way, if you make a mistake during your attempts to
recover data, you can make another copy of the clone instead of having to
spin up the failing disk again.

Robert Trevellyan


On Sat, Jul 13, 2019 at 6:16 AM David Morrison <address@hidden>
wrote:

> I have been given a WD Thunderbolt Duo device which has intermittent
> problems. From what I can see, it connects two SATA disks (3TB each)
> to a Mac using Thunderbolt.
>
> However, OS X allows multiple disks connected to a Mac to be set up
> using software RAID. The owner was told this one had been set up to
> mirror the two disks, which theoretically gave it a capacity of 3TB
> with a certain amount of redundancy.
>
> Unfortunately, it turns out to be set up as a single 6TB volume
> striped across both disks.
>
> And even more unfortunately, I have discovered that one of the disks
> has a lot of bad blocks. The 6TB volume mounts fine, and a lot of
> files can be copied off it. However, a lot of files give errors in
> the Mac Finder. If possible, I would like to recover those files
> (family photos) so was thinking of using ddrescue to try to recover
> those bad blocks.
>
> Now I can see two approaches. One would be to copy the failing 3TB
> disk, then try to put the RAID volume together again using the copy
> and the other original disk. Is the RAID system likely to accept this?
>
> The other is to copy the entire 6TB volume, depending on whether
> ddrescue can work on a RAID volume. Can it? (And I would have to get
> a 6TB disk.)
>
> I would be grateful for any thoughts on the best approach, and
> anything else I need to know.
>
> Thanks
>
> _______________________________________________
> Bug-ddrescue mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/bug-ddrescue
>