[plug] Data recovery with Gentoo system rescue cd

[Craig Ringer]

On Fri, 2004-07-23 at 16:04, caston at arach.net.au wrote:

> I'm sure sure if there is an issue with these drives but I was using a 
> hardcano 11 and felt that the drive temp was usually above what it should be. 
> I watched it climb to 35degrees at the installfest.

35 degrees seems pretty normal to me. That's where my RAID disks in my
server at work sit normally, but they can climb to more than 45 degrees
under heavy load. My home desktop's disks tend to be more like 25
degrees, but then they're very well cooled and doing very little.

> A few questions:
> 
> Would it be worth using dd to dump the entire drive contents to the new drive 
> or should I rebuild from scatch? 

dd will get you a more exact copy (down to the same inode numbers etc),
but chances are that doesn't matter. When migrating data off failing
disks I tend to use dd where possible because it's fast and easy.

If dd cannot read some sectors and fails, it is probably safer to make a
new filesystem on the target and copy all the files instead ('cpio -p'
is good for this) rather than using dd with conv=noerror.

> What is the dd command and block size I should use?

I find that bs=1M (or more) massively improves the transfer rate. 
Otherwise, a normal

dd if=/dev/source_device of=/dev/target_device bs=1M 

should do nicely. I would recommend building a new partition table on
the new disk and doing partition-by-partition copies rather than trying
to copy the entire disk, as I've seen some odd results with full disk
copies in the past. 

You will need to reinstall the boot loader on the new disk, too.

Of course, with this sort of thing there is no one "right" way, and in
the end so long as you get your data off safely it's good enough.

--
Craig Ringer