Fedora and LVM [LWN.net]

Fedora and LVM

Posted Nov 2, 2012 0:19 UTC (Fri) by dlang (✭ supporter ✭, #313)
In reply to: Fedora and LVM by Tobu
Parent article: Fedora and LVM

the question is which issue do you run into more frequently

the need to resize anything other than the last partition on a disk (or have a filesystem span multiple drives)

the problames caused by LVM

for many of us, the cases where LVM would be useful are much more rare than the cases where LVM is a problem.

I almost never resize partitions after the system is created (especially on production systems)

I would not WANT to have a single filesystem that spanned multiple drives, that's what's known as RAID 0, and it means that if _either_ drive has problems, I can loose the entire filesystem.

meanwhile, the downsides have caused me problems more than once (including cases with colo systems where a drive has partially failed, the facility has replaced the drive and then 'helpfully' plugged in the old drive, now both have default LVM configs and the system is unusable)

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Fedora and LVM

Posted Nov 2, 2012 0:46 UTC (Fri) by Tobu (subscriber, #24111) [Link]

That's “often” in the first column, and “huh?” in the second. The functionality is pretty basic and I've found it reliable. Most of my experience is from a desktop (long-lived in the same way as Theseus' ship).

That said, I don't mind learning from your colo problem. What made it hard to fix? Was the collision on UUIDs or logical names?

Fedora and LVM

Posted Nov 2, 2012 1:13 UTC (Fri) by dlang (✭ supporter ✭, #313) [Link]

I think it was in logical names (others in this thread have mentioned being hit by that problem as well)

Fedora and LVM

Posted Nov 2, 2012 7:49 UTC (Fri) by Cato (subscriber, #7643) [Link]

I've seen similar issues on mailing lists when a hard disk from one Fedora machine is plugged into another Fedora machine - since they both use the default VG and LV names, much confusion results and it's not easy to recover from.

One tip for using LVM is to never use the default VG and LV names, to avoid this sort of thing.

I've lost far more time (and data) due to LVM complexities/issues than I have saved through easy expansion/moving of FSs. It makes upgrades and transferring to new PCs much more complex.

Fedora and LVM

Posted Nov 2, 2012 13:07 UTC (Fri) by Tobu (subscriber, #24111) [Link]

I've just tried it (using a VM to create a colliding VG name, then kpartx -a to make the nested partitions show up).

$ sudo pvscan
WARNING: Duplicate VG name V2: Existing 5daecde1-e30c-4ef8-bcf6-e501382f67b7 (created here) takes precedence over 8b814833-1a37-47d4-896d-5a8aa74f458f
  PV /dev/mapper/sda2p1   VG V2     lvm2 [1016,00 MiB / 0    free]
  PV /dev/sda5            VG V2     lvm2 [1,82 TiB / 13,00 GiB free]

$ sudo vgrename 8b814833-1a37-47d4-896d-5a8aa74f458f V3
  Volume group "V2" successfully renamed to "V3"

Accessing the partition was very easy, but then I had to edit the root= boot parameter to boot the VM (vgcfgrestore to undo the rename would also work). This could be improved by having root= be uuid-based (which Debian/Ubuntu don't do for LVM, don't know about Fedora), as well as by having the Fedora installer pick a more unique VG name.

Debian and Ubuntu pick the hostname as the VG name, this seems like a good way to prevent these collisions entirely.