PGP SIGNED MESSAGE
Hash: SHA1
Hi, I encountered a very serious bug with LVM today. I'm using
lvm2-2.01.04-5 from Debian stable, kernel 2.6.17-rc3
# lvm version
LVM version: 2.01.04 (2005-02-09)
Library version: 1.01.00-ioctl (2005-01-17)
Driver version: 4.6.0
What I did:
* created a LV in an LVM1 VG using EVMS (yeah, I know) with a
space in the name (yeah, yeah, I know, I know :-));
* converted the VG to LVM2 using vgconvert;
* as a result the space in the LVM1 metadata was converted over
into a space in LVM2 textual metadata, which causes a nice
"Parse error line 123" for every subsequent LVM command on that
VG, including "vgcfgrestore"
course I did that on the root VG of my work laptop (Backups? What
backups?) and ended up in the aforementioned pickle. I tried some dd
stunts to overwrite the space with a dash, having discovered the
correct offset and block size with strace() (which for the record were
respectively one block and 2560 bytes, YMMV) - But bummer, some
wiseguy put a CRC32 checksum in there! :-) I had to recompile a custom
version of lvm that passes NULL as the checksum_fn parameter to
text_vg_import_fd (again for the record, that's a trivial one-line
patch in function _vg_read_raw_area, in format-text.c around line 286).
The situation definitely needs some fixing. My humble suggestions:
* vgconvert should surface-test the LVM1 metadata as strictly as
the command-line "lvcreate" tool does on its arguments;
* there should be a mechanism for dealing with corrupt LVM
metadata, at the minimum a global command-line switch to
temporarily disable checksum verifications.
Now investigating backup software *real seriously* :-) Thanks for your
work on the Linux LVM suite,
- --
Dominique QUATRAVAUX I senior
01 44 42 00 08 IDEALX
PGP SIGNATURE
Version: GnuPG v1.4.1 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org
zzsNGFC6lPaRBvpRy2am/TM=
=ad0C
PGP SIGNATURE
linux-lvm mailing list
linux-lvm (AT) redhat (DOT) com
read the LVM HW-T at http://tldp.org/HWT/LVM-HWT/

PGP SIGNED MESSAGE
Hash: SHA1

Alasdair G Kergon wrote:

I should add that what you should do is extract the metadata you've
retrieved off disk directly into a file, fix it in the file
(differences in whitespace & comments don't matter) then use
vgcfgrestore -f.

I tried that and it works - strange, I tried vgcfgrestore yesterday to
no avail But then I was using Ubuntu 5.10's lvm2 package as a
rescue so apparently it's a different (and solved) issue. Thanks!

Knowing this, and still for the record: after any LVM operation it
seems wise to try a vgchange -a y *before* rebooting to see if
everything went well. Reverting a pickled LVM situation is much easier
with the original toolset handy (same LVM binary and metadata backups
in /etc/lvm/) than using a rescue CD!

I wrote, and you replied:

>* there should be a mechanism for dealing with corrupt LVM
>metadata, at the minimum a global command-line switch to
>temporarily disable checksum verifications.
>
Nope.

I seem to have pushed your button, apologies for doing so. I was
trying to be humorous, not disparaging: *of course* I concur that
checksums are a good idea! I guess it means that humor is too slippery
for us non-native speakers, oh well
- --
Dominique QUATRAVAUX I senior
01 44 42 00 08 IDEALX

PGP SIGNATURE
Version: GnuPG v1.4.1 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

R2b4HLcvmPmWHl+uxhbvGi0=
=tWX0
PGP SIGNATURE

linux-lvm mailing list
linux-lvm (AT) redhat (DOT) com

read the LVM HW-T at http://tldp.org/HWT/LVM-HWT/