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Date:      Fri, 28 Aug 1998 22:11:08 +0000
From:      Mike Smith <mike@smith.net.au>
To:        Brian Behlendorf <brian@hyperreal.org>
Cc:        freebsd-scsi@FreeBSD.ORG
Subject:   Re: medium error 
Message-ID:  <199808282211.WAA00589@word.smith.net.au>
In-Reply-To: Your message of "Fri, 28 Aug 1998 19:04:01 MST." <19980829020856.14746.qmail@hyperreal.org> 

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> 
> (please include my address in responses, I'm not on -scsi)
> 
> I had a disk go bad on me while installing a new one - unfortunately it had
> a few things on it that are worth trying to salvage the disk for (items
> that backups didn't save).  At this point all I'm getting when I try to
> talk to it is "Medium format error - device not configured" errors to the
> console, although the SCSI card can identify it properly, even get the
> manufacturer & model #.

These parameters are usually in nonvolatile memory, not on the disk, 
although there is often a second firmware component loaded off the disk.

> All tools, from disklabel to fdisk, fail to do
> anything, causing the above error message.  Am I outta luck?  Is it beyond
> the OS at this point?

It looks like the disk is damaged in a fashion that's making it 
impossible to obtain slice and/or label information.

Recovery at this point is problematic, but may not be impossible,
depending on how much time and effort you are willing to put into the
process, and how lucky you are.

To start with, try writing a simple program which just opens the bare
device (eg. /dev/sdX).  If the open completes OK, then you should be 
able to improve the program to build an image of the entire disk in a 
file on another disk.  You will have to read the device one block at a 
time, and note whether you succeed or fail.  It's possible that the 
disk may go offline after a failure, so you may need to further improve 
the program such that you can reboot and take up where you left off.

If you are unable to open the bare device, then you should check with 
the scsi(8) command as to whether you can read a single block from the 
drive.  This will involve some familiarity with SCSI commands.  If this 
works, then you should build a program as described above, but use raw 
SCSI commands rather than device I/O to talk to the drive.  The chances 
of this sort of program working are only slightly better than the first.

If you are able to recover most of the disk, you will then need to 
reconstruct the missing blocks as required to recover your data.  
Needless to say, you should make a backup of the image file before you 
start.  Start by reestablishing the MBR (if the disk had one), and then 
the partition table(s) in the slices.  If you can't remember what the 
table(s) looked like, search the image file for the filesystem magic 
numbers to find the beginning of your partition(s).

This can be complicated if the top of a filesystem has been damaged; 
you will have to locate an alternate superblock, work out from that 
where the base of the filesystem was, reconstruct and then use fsck -b.

>  Are there any shops in the Bay Area that will
> re-seat the platters into a new drive housing for a reasonable fee?

Without knowing the FRU out of the vendor-specific data from the SCSI 
error codes, and having the FRU list for the disk in question, it's 
difficult to know whether this would be worth the effort.

There are a number of such organisations; check your copy of 
MicroTimes as I'm fairly sure that several of them advertise there 
regularly.

> This was a Seagate 15230N, by the way.

Hmm, that's fairly odd.  These (Hawk 4) are normally pretty solid; I
presume you *were* keeping it cool? 8)

-- 
\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com



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