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[linux-lvm] LVM2 setup notes and questions



  Just got finished making device-mapper 0.96.03 work with RedHat Limbo
beta2, LVM tools 2.1.95.10, kernel 2.4.19-r7 from gentoo, and raw two
drives as one physical volume and one logical volume. Ran into a few
gotchas, but I was able to workaround them all.

  The first problem was with make apply-patches not finding the patches
because I told it I was using 2.4.19 during configure instead of
2.4.19-rc1. I fixed this by changing the version line in the Makefile.
The second problem was simple rejects during running make apply-patches.
They were caused by small differences in the gentoo kernel. It only
required changing a few words on 3 lines. After that I recompiled the
kernel with device-mapper support. I built a rpm of the device-mapper
library with checkinstall. Then I moved on to LVM2 tools which gave me a
number of hassles. After compiling it I used checkinstall to make an rpm
of it. The first was vgscan and vgchange being linked to readline and
the readline libraries being in /usr/lib, but rc.sysinit was trying to
run them before /usr was mounted. At first I didn't read closely and
staticly linked libdevmapper thinking it would make the whole program
staticly linked. That didn't help, so I checked ./configure --help again
and find the option to disable readline. In the middle of this I ran
devmap_mknod.sh once to setup whatever devices vgscan and vgchange
wanted. I would suggest a mention in the README about
--disable-readline. I used --disable-readline and it fixed the library
problem. Then I had a problem with "setlocale failed". I did a Google
search and found mention that other programs worked when LANG was LANG=C
instead of LANG=en_US so I added a workaround to the rc.sysinit. 

TLANG='$LANG'
LANG='C'

before the vgscan and vgchange and

LANG='$TLANG'

after.

I think this may relate to RedHat switching to UTF-8 in Limbo betas and
at that point in the boot process all of the environment isn't setup.
The next problem I ran into was a common one of vgscan trying to scan
cdrom drives at hda and hdc. After reading the man page for lvm.conf and
doing a little Google searching I figure out the correct format to
filter both. I think the man page could use some additional examples to
show the format for more than one filter. The final problem I ran into
once the volume group was being activated was the device name change
from /dev/vg/data to /dev/device-mapper/vg-data   So I had to modify it
in /etc/fstab   I like the change so that all volume devices will be in
the same directory, it adds consistency.

  The reason I converted from LVM1 to LVM2 is so that I could recover
data if one of the drives failed. Since I only don't plan to snapshot or
move I don't forsee many problems. I do think that the LVM project
should make the statement of LVM1's lack of recovery of a logical volume
if one of the drives fails more known and obvious.

  Now I have some questions. What are the steps involved in recovering
should either of my drives fail? How do I convert the metadata from LVM1
format to LVM2 format? Is there a reason I would want to or not want to?
If I wanted to add a partition on a third drive would it be as simple as
adding it to the physical volume group and then used parted resize the
filesystem? Is there a tool in the LVM2 packages that will do the same
thing that parted does for ext3? Any bugs known in device-mapper 0.96.03
that would make it a good idea to upgrade to the CVS version? Any other
things any of you think I should know about LVM2?




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