Mounting an LVM disk

Weiner, Michael weinerm at ccf.org
Mon May 24 15:39:09 CDT 2010


I appreciate the advice and suggestions provided, and I am in the
process of 'fixing' the problem, so this shouldn't happen again.
Fortunately I think the solution is far easier than I would have
thought. I shut the server down and pulled the new 2Tb OS disk, and
replaced it with the trouble disk (old 1Tb OS disk) and turned  the
server back on. Of course the Perc complained loudly about the disks
being a 'foreign configuration' 
As I had expected, so I went ahead and thought I could simply 'import'
the configuration but wasn't able to do that as the function was 'greyed
out.' So I 'cleared' the configuration and then recreated the single
disk for the OS and the 4 disk RAID0 and rebooted the server. The old
disk is up and running, though I am somewhat surprised. I am in the
process of syncing the $HOME directory off at this point. 

Most of the LV commands (vgscan, lvmdiskscan, etc) really weren't able
to see the disk, and I am still somewhat confused as to why an fdisk was
seeing a 2Tb disk when it is really a 1Tb disk, and why there was no
partion table to read, but at the moment, I am able to get off what I
need ... so I will have to determine that cause after I complete this
process.

Just in case you are wondering, we are only using a single disk for the
OS and RAID0 for the rest because this is a research environment with no
funding other than what comes through Grants, and unfortunately this is
what we can afford. This server is used for data analysis of sequencing
data using the Illumina Pipeline software, and the actual owner of the
server understands the short-comings of the hardware configured in this
way, but suffice it to say, that the individual wanted a boat-load of
processing power and memory with lots of local disk space. So a Dell
PowerEdge R910 was purchased with 4 Quad core processors, 32G RAM, and
(now) 5x2Tb disks giving 1 disk for OS and the other 4 for 8Tb for data
storage using RAID0 hanging off the Perc 6/i controller. This is only
one piece in the workflow, and actually one of two servers in this role.
He has a second server that serves the same purpose, but it is a PE2870.
We had the data synced off to a temporary repository, but hadn't done
the same with the $HOME directory - nor purchased a license and setup
NetBackup as we normally would. I am not particularly happy with the
design, but it is what I have to live with :(

Thanks again for the suggestions, I did a mash-up of several of them and
got this resolved I believe.

Michael

-----Original Message-----
From: linux-poweredge-bounces at dell.com
[mailto:linux-poweredge-bounces at dell.com] On Behalf Of Jefferson Ogata
Sent: Monday, May 24, 2010 4:00 PM
To: linux-poweredge at dell.com
Subject: Re: Mounting an LVM disk

On 2010-05-24 19:09, J. Epperson wrote:
> Some good points, but having had this hole in my own foot, I'll say
that
> it's very unlikely that it's _just_ the partition table that got
wiped.  I
> also never had any luck getting a partition editor to work with a disk
> that had a table saying it was bigger than it actually was.  Always
had to
> wipe it at a hardware level to get it repartitioned.
> 
> I hope OP's luck is better.

OP doesn't need a partition table. Assuming that a dd was executed in 
the wrong direction for some period but aborted without wiping out too 
much of the disk, he needs to know the offset where the /home filesystem

started, and a lower bound on its size. The filesystem could start at 
any multiple of LVM chunk size from the beginning of the physical 
volume, which would have covered either the entire disk (which may still

be what's going on) or have started at a track offset from the start of 
the disk, or cylinder offset if not on the same cylinder as the 
partition table or logical partition table (unless the disk was 
partitioned in some unusual way). If not too much of the disk is gone, 
he also might be able to find a backup of the LVM config somewhere. It 
would be worthwhile imaging the whole disk as a backup, and using 
strings(1) to try to find an LVM backup.

A bigger question for me is why the OP isn't using any redundancy 
(single disk for OS and RAID0 for the rest), but whatever...

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