Tag Archives: LVM

When LVM volume groups collide

I took my hard drive and connected it to another computer with Linux installed. Both HDs had a PV which contained a VG named “vg00”. This collistion was the first time I had encounterd this situation and had to solve it to get access to files on both VGs.

During boot I noticed messages saying there two vg00 on the machine and one is taken precedence over the other. Example message:

[lvm] WARNING: Duplicate VG name vg00: Existing
K0qKAk-Ph5i-BcAX-y4yp-SPF3-TZgj-DufR3L (created here) takes precedence
over K0qKAk-Ph5i-BcAX-y4yp-SPF3-TZgj-DufR3L

The trivial solution is to rename the extra VG to something different and get the access I want to the files. But there are two problems:

  1. As the first vg00 has precedence, I can’t do actions on the second one. The LVM commands ignore the second one.
  2. I can’t act on the first VG as it’s active for most of the system’s file systems.

Trying vgrename command with the second VG UUID didn’t work. I had to deactivate the first VG first (luckily I have the root FS outside of LVM), rename it, and rename the second VG and then rename the first VG again.

This resulted in having vg00 and vg01. And now I could activate them both and access the files.

I hope to have the time to reproduce the problem on another distro to make sure that’s a general LVM2 problem. Having renmae by UUID would save time to fix the problem and help people who need to boot from CD just to get their VG deactivated (since root FS is on LVM).

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Filed under Debian GNU/Linux, Red Hat Enterprise Linux

Who moved my PEs (or why does pvmove sucks on linux) ?

Yesterday I wanted to extend an existing LVM VG with some central storage disks. In the process, I notice the VG is built upon local & external disk, which isn’t according to my standards.

So I decided to extend the VG with the external disks, and then use pvmove command to move all the PE from the internal disk before reducing the VG. The problem is, that on RHEL 4.4, the pvmove command hangs during it’s work, never returns to the prompt, and locks all the other LVM commands.

Seems that for little amounts of PEs the command works, but for 10G disks it hangs. As nothing else helped, I was forced to hard boot the server using to power button. Running the command in single user also doesn’t effect the result, although non other user/services are running.

RHEL 4.4 has LVM2 version 2.02.06, RHEL 4.5 has version 2.02.21 and RHEL 4.6 has version 2.02.27. Reading upstream’s changelog seems there isn’t any change regarding pvmove, although it’s still worth testing if upgrade helps.

Version 2.02.29 has “Refactor pvmove allocation code” in its changelog, but it will take time before this version will be officially available for RHEL (fedora 8 only has 2.02.28). Hoepfully it will solve the problem, as my HP-UX colleagues are laughing on my expense… And that I have to invest more time in mimicking pvmove work manually.

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Filed under Red Hat Enterprise Linux