Minor disaster recovery

[Ben Scott]

On Wed, Aug 12, 2009 at 8:16 AM, Tyson Sawyer<tyson at j3.org> wrote:
> The filesystem on the system drive is (or should be) backed up.

  You need to explain that using a lot more words.  :)

  (e.g., how you back it up, using what software, how often, what you
backup, how you test the backups, when your last backup was made,
what's changed since then, etc.)

> We would like to recover the system rather than rebuild to avoid having
> to figure out all the applications we had installed and figure out how
> we had them configured.

  As Jim Kuzdrall said, I would avoid trying to run a system copied
from a drive that's known to be faulty.  You might copy a corrupt
file.

  If you have a known-good backup of the system, from before the disk
started to fail, restoring *that* to a new disk and running is okay.

  (I don't think Ubuntu keeps checksums of installed files by default
(anyone know?).  So there's no way to verify the integrity of the
installed system (like "rpm --verify --all").  And even with package
manager checksums, that won't help you with corrupt data files, config
files, or files installed outside of the package manager ("make
install").)

> There is a reasonable chance that we can
> reboot the old drive again, but I have not yet tried.

  Don't try.  As Jeff Smith said, the more you tinker, the worse
things usually get.

  If you intend to attempt to recover data from the failed disk, I
would suggest making a block level image, like Jeff said.  But I'd
recommend using the "dd_rescue" and "dd_rhelp" utilities to do so.
dd_rhelp will supervise dd_rescue, and use it to recovery easily
readable blocks first, and then try harder for the remaining blocks.

  Once you've got the block-level image, you can examine it at your
leisure, without worrying about if the drive is about to die for good.

> We will attempt to find a replacement drive today.  We live in
> Brookline, NH and work in Bedford, MA.  Any suggestions on stores or
> drive brands?

  All hard disk drive brands are about equal.

  All big stores are about equal.  Staples, OfficeMax, Wal-Mart, etc.

  Or find a local guy.  For buying commodity parts, parts is parts,
but some find it nice to give business to the little guy, and having a
good relationship with a local tech dealer is a useful thing for a
home user.

> ... boot the old drive with the new as a secondary.  ... Copy
> the filesystem from the old to the new.

  I wouldn't recommend that no matter what.

  If I was going to copy a system from one disk to another, I'd put
both drives in the system, boot from CD, and copy that way.  Copying a
running system is best avoided.

  But I wouldn't try to copy the install, for reasons given above.

  If I had a *complete* and *known-good* backup of the old system, I'd
boot from CD, then restore that backup to the new disk.  I might then
try and recovery anything that's changed since the last backup.

  If I wasn't sure about my backup, or it wasn't complete: I would
install a clean copy of my OS on to the new drive, from a known-good
CD.  Get up and running with a working system.  Then I'd copy and/or
restore stuff from backups and/or the old drive.

-- Ben