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# df -h /srv/files/
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_critical-lv_files
6.9G 4.6G 2.1G 70% /srv/files
CAUTION
Resizing filesystems
Not all filesystems can be resized online; resizing a volume can therefore
require unmounting the filesystem first and remounting it aerwards. Of
course, if one wants to shrink the space allocated to an LV, the filesystem
must be shrunk first; the order is reversed when the resizing goes in the other
direction: the logical volume must be grown before the filesystem on it. It's
rather straightforward, since at no time must the filesystem size be larger
than the block device where it resides (whether that device is a physical partition
or a logical volume).
The ext3, ext4 and xfs filesystems can be grown online, without unmounting;
shrinking requires an unmount. The reiserfs filesystem allows online resizing
in both directions. The venerable ext2 allows neither, and always requires
unmounting.
We could proceed in a similar fashion to extend the volume hosting the database, only we've
reached the VG's available space limit:
# df -h /srv/base/
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_critical-lv_base
# vgdisplay -C vg_critical
1008M 835M 123M 88% /srv/base
VG #PV #LV #SN Attr VSize VFree
vg_critical 2 2 0 wz--n- 8.14g 144.00m
No matter, since LVM allows adding physical volumes to existing volume groups. For instance,
maybe we've noticed that the sdb1 partition, which was so far used outside of LVM, only contained
archives that could be moved to lv_backups. We can now recycle it and integrate it to the
volume group, and thereby reclaim some available space. This is the purpose of the vgextend
command. Of course, the partition must be prepared as a physical volume beforehand. Once the
VG has been extended, we can use similar commands as previously to grow the logical volume
then the filesystem:
# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created
# vgextend vg_critical /dev/sdb1
Volume group "vg_critical" successfully extended
# vgdisplay -C vg_critical
VG #PV #LV #SN Attr VSize VFree
vg_critical 3 2 0 wz--n- 9.09g 1.09g
# [...]
316 The Debian Administrator's Handbook