Here’s one for the hall of fame of terrible error messages.

When trying to add a mirror to a LVM volume on a linux box, you get this message:

#lvconvert -m 1 disks/root /dev/sdb2

Not enough PVs with free space available for parallel allocation.
Consider --alloc anywhere if desperate.

This message is completely useless, we have TONS of free extents on both disks. So we check for help

# lvconvert
Exactly one of --mirrors or --snapshot arguments required.
lvconvert: Change logical volume layout

lvconvert [-m|--mirrors Mirrors [--corelog]]
[-R|--regionsize MirrorLogRegionSize]
[--alloc AllocationPolicy]
[-d|--debug]
[-h|-?|--help]
[-v|--verbose]
[--version]
LogicalVolume[Path] [PhysicalVolume[Path]...]

Yea. Not much that is obvious there we can work with. So after hitting (1) forehead and (2) Google, we discover in an obscure blog reply that we need to specify where the mirror log goes for this.

Well it would have been nice to have that in the “help” message, or the HOWTO, or the Guide and probably in the error message as well now wouldn’t it.

So for you seekers out there, here is what you need to do. Just throw in that one extra option in the help message that doesn’t have much explanation:

lvconvert -m 1 disks/root /dev/sda2 --corelog

Logical volume root converted.

Yes, just adding –corelog will do the job. This tells it to keep the log in RAM, so yes you’ll have to rebuild the array after a reboot.

If you’re creating a new volume and you get this error, try tacking –corelog on the end of that command as well.

Doesn’t look like LVM folks accept direct bug reports either, maybe you can pass the word along?