[svlug] scsi troubleshooting

J C Lawrence claw at kanga.nu
Sun Dec 2 23:53:02 PST 2001

On Mon, 3 Dec 2001 02:42:18 -0500 
step1b  <S> wrote:

> Quoting J C Lawrence (claw at kanga.nu):
>> On Mon, 3 Dec 2001 01:59:04 -0500 step1b <S> wrote:
>> > SCSI device sda: hdwr sector= 512 bytes. Sector= 17916240 [8748
>> > Mb] [8.7 Gb] sda: unknown partition table
>> Something in your partition table is host.  most likely this
>> means that something within either the first 512 bytes or 1Meg of
>> your disk was whacked.
>> You do have a backup of your partition table don't you?

> no i dont have it, any alternative ?

Do you have good record of the exact sizes of the various partitions
and their sequence?  Occasionally (some say often) you can get away
with using that to waffle stomp an assumed correct partition table
on the device.

If you have neither, then you're in for a job of some hours if not
small order days (depending on how bad it is) working thru the disk
with a sector editor piecing the bits back together (actually most
of your time will be spend finding the bits to piece together).  

  ObNote: If you're very (make that extremely) lucky the entire
  problem will be that the signature block on your partition table
  got hosed and simply replacing that will bring everything back to
  glory.  A job of a few minutes to detect, another few minutes to
  verify, and a couple minutes to correct.

> well that system was setup by somebody else, and i dont have any
> info about its partitions. Can something still be done ?

Yup, it just gets painful.  I'd start out first trying to find out
exactly what the partition table was, and if you can't get that, get
as close as you can.  The more data you have the less disk sectors
you'll have to search thru looking for signature patterns (eg the
starts and ends of filesystems, superblocks, extended partition
tables, etc).  It makes the job that much easier and faster.

  ObNote: Just because the partition table is bad doesn't mean that
  the rest of the disk isn't bad/dead/deleted as well.  This is not
  intended to scare you but to prompt you into thinking about
  exactly how valuable your data is and how much time and effort you
  are going to involve in its recovery.

  If the problem turns out to be non-trivial you may seriously want
  to consider enlisting the aide of a professional data recovery

This is also a good time to rant about the value of regularly,
tested and verified restorable and correct backups, but I'll let
someone else do that.

J C Lawrence                
---------(*)                Satan, oscillate my metallic sonatas. 
claw at kanga.nu               He lived as a devil, eh?		  
http://www.kanga.nu/~claw/  Evil is a name of a foeman, as I live.

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