Linux – Resizing logical volume with no free extents but with free disk space

linuxlvmxfs

I have a 7.9 TB logical volume formatted with XFS filesystem. I have 8 1 TB RAID devices as physical volumes, and 1 volume group that contains all of these devices. I have 2.5 TB free space on my logical volume. I'd like to remove 2 of the 1 TB devices from the volume group since I don't "need" them anymore. Reading the man page of pvmove, it seems like I would need to create at least 5.5 TB of space and pvmove everything from the current 1 TB volumes onto the new volumes, and then remove all 8 of the original volumes from the logical volume. This seems onerous. Any suggestions?

Best Answer

There's no problem on the LVM side. Use lvreduce to shrink a volume group; obviously, if there's a filesystem on it, you mustn't shrink it below the size of the filesystem. Then use pvmove to shuffle extents around: pvmove /dev/sdz42 removes extents from the physical volume /dev/sdz42 to other physical volumes in the same volume group, after which you can decommission the physical volume with vgreduce.

However this is moot since you have an XFS filesystem, and XFS does not support shrinking. I'm afraid you'll have to move the data off and remake the filesystem (and thus you can be completely unsubtle with LVM).

Related Solutions

Create a volume group from a logical volume instead of a physical volume

Yes, it is possible, though you are adding complexity.
I would use this approach either experimentally or as a last resort, only after you have explored other solutions.

paraphrasing man pvcreate "pvcreate initializes PV for later use by the LVM. Each PV can be a ... or meta device ...

Apparently an LV qualifies as a meta device.

Empirically speaking, the following worked just fine

pvcreate /dev/sda16
vgcreate demo /dev/sda16
lvcreate --name lv -l '100%VG' demo
pvcreate /dev/mapper/demo-lv  
vgcreate wrappervg /dev/mapper/demo-lv  
lvcreate --name lv -l '100%VG' wrappervg  
mkfs.ext4 /dev/mapper/wrappervg-lv  
mkdir /mnt/wrapper  
mount /dev/mapper/wrappervg-lv /mnt/wrapper  
touch /mnt/wrapper/foo

Linux LVM – Moving Logical Volume to a New Physical Disk

One volume group solution:

 pvcreate /dev/sdb
 vgextend vg0 /dev/sdb
 pvmove -n /dev/vg0/bar /dev/sda /dev/sdb

Two volume group solution:

 pvcreate /dev/sdb
 vgcreate vg1 /dev/sdb
 lvcreate -l100%FREE vg1
 mkfs -t ext4 /dev/vg1/lvol1
 mount /dev/vg1/lvol1 /mnt

Now difficult part, all activities MUST stop on /bar:

 cd /mnt ; ( cd /bat ; tar cf - * ) | tar xf -
 cd /
 umount /mnt
 mount /dev/vg1/lvol1 /bar

where

pvcreate erase all data on disk (and prepare for LVM)
lvcreate sould create a logical volume lvol1, you specify lv name with -n bar
I use HP-UX syntax for lv, you might have to use /dev/mapper/myvg-mylv syntax

Once you have verified data are OK, in new place:

you can safely delete old /bar
edit /etc/fstab to use new /bar

Best Answer

Related Solutions

Create a volume group from a logical volume instead of a physical volume

Linux LVM – Moving Logical Volume to a New Physical Disk

Related Question