Daniel Hill wrote, On 16/09/09 20:10:
don't like articles that don't state what they are trying achieve or
what LVM does
LVM is another layer of indirection for disk storage. Allows you to
expand the LV a filesystem lives on, without having to shuffle
partitions on disk like the OP. Most filesystems these days support
some kind of expand function. Some do it live, and some even can be shrunk.
You have Physical Volumes (PV), which are one or more partitions, that
are combined to form Volume Groups (VGs) and inside a PV you create
Logical Volumes (or LVs).
Example
[r...@server ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/md1 2.8G 2.1G 599M 78% /
/dev/md0 97M 22M 71M 23% /boot
/dev/mapper/VG00-home 157G 129G 20G 87% /home
/dev/md2 5.8G 1.3G 4.3G 23% /usr
/dev/md3 29G 19G 9.3G 67% /var
/dev/mapper/VG00-imap 50G 16G 32G 33% /var/spool/imap
[r...@swerver ~]# pvdisplay
--- Physical volume ---
PV Name /dev/md4
VG Name VG00
PV Size 421.95 GB / not usable 448.00 KB
Allocatable yes
PE Size (KByte) 4096
Total PE 108019
Free PE 54594
Allocated PE 53425
PV UUID CLxPXr-BC7N-vv3H-vs06-UcuA-etdo-tk7DNT
So there's 54594 blocks of 4MB (~220GB) which could be allocated to new
LVs or appended to existing ones
[r...@sever ~]# lvdisplay
--- Logical volume ---
LV Name /dev/VG00/home
VG Name VG00
LV UUID 000000-0000-0000-0000-0000-0000-000000
LV Write Access read/write
LV Status available
# open 1
LV Size 158.59 GB
Current LE 40600
Segments 2
Allocation normal
Read ahead sectors 10000
Block device 253:0
--- Logical volume ---
LV Name /dev/VG00/imap
VG Name VG00
LV UUID 000000-0000-0000-0000-0000-0000-000001
LV Write Access read/write
LV Status available
# open 1
LV Size 50.10 GB
Current LE 12825
Segments 1
Allocation normal
Read ahead sectors 10000
Block device 253:1
Note the home LV has 2 segments - it has already been expanded once.
Note also that LVM is not RAID. LVM provides only convenience, and no
additional reliability in itself.
--
Craig Falconer
