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Re: xfs_repair force_geometry

To: benediktibk@xxxxxx
Subject: Re: xfs_repair force_geometry
From: "Michael L. Semon" <mlsemon35@xxxxxxxxx>
Date: Mon, 13 May 2013 12:58:36 -0400
Cc: Benedikt Schmidt <benedikt.schmidt@xxxxxx>, xfs@xxxxxxxxxxx
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Ordinary user comments follow...

On 05/13/2013 08:24 AM, Benedikt Schmidt wrote:
Hi,
currently I'm looking for the correct usage of the force_geometry option
of xfs_repair. I wasn't able to find more documentation on this option
beside that it exists. Could please somebody explain it to me?

According to the xfs_repair man page, it just means to skip the geometry test. In other words, it's not a place to place CHS values or specify that your new drive has 4k sectors. Usage is '-o force_geometry'.

For a more detailed description of my problem: I've got here a hard disk
which is dying at the moment, so I copied all the content with dd_rescue
to a new and bigger one. To use xfs_copy wasn't possible as the
filesystem was already corrupted. So now I've got nearly everything on
the second hard disk (dd_rescue could'nt copy something around 6 or 7
MB), but I can not mount the filesystem or even run xfs_repair on it, as
it fails to find a superblock. I think the problem lies in the fact that
the new disk has a different geometry than the previous one.

Kind regards,
Benedikt Schmidt

Did you ddrescue to a regular file or to a new partition? In my case, ddrescue didn't let me do a simple `ddrescue /dev/sda8 /dev/sdb6`, so I passed on using ddrescue's suggested '--force' flag and instead did something like this:

root@plbearer:~# ddrescue /dev/sda8 /mnt/xfstests-test/fs_as_file

GNU ddrescue 1.16
Press Ctrl-C to interrupt
rescued:   671088 kB,  errsize:       0 B,  current rate:    9043 kB/s
   ipos:   671023 kB,   errors:       0,    average rate:   31956 kB/s
   opos:   671023 kB,     time since last successful read:       0 s
Finished

# -f means "check a regular file"
# -n means "do not modify filesystem"
root@plbearer:~# xfs_repair -f -n -o force_geometry /mnt/xfstests-test/fs_as_file
Phase 1 - find and verify superblock...
Phase 2 - using internal log
        - scan filesystem freespace and inode maps...
        - found root inode chunk
Phase 3 - for each AG...
        - scan (but don't clear) agi unlinked lists...
        - process known inodes and perform inode discovery...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - process newly discovered inodes...
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
No modify flag set, skipping phase 5
Phase 6 - check inode connectivity...
        - traversing filesystem ...
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify link counts...
No modify flag set, skipping filesystem flush and exiting.

root@plbearer:~# mount -t xfs -o loop /mnt/xfstests-test/fs_as_file /mnt/loopback/

With the regular file mounted loopback, this is the part where I would somehow get the data to a freshly-made XFS filesystem somewhere else, then verify that the data that I need is indeed still intact and valid. There are lots of tools to do such operations. I lean on xfsdump/xfsrestore because I have longstanding good experience with the programs and see such situations as a really bad time to learn new tools.

If this is your last copy of important data, you should a) use the '-n' flag of xfs_repair before deciding to modify the ddrescued filesystem, and/or b) duplicate your recovered filesystem to another place so you have at least one good emergency backup.

Good luck, and be careful!

Michael

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