This tip shows you how to grow the existing disk in rootvg without any outage on the AIX logical partition.
It's important to have enough spare disk in rootvg -- the AIX OS volume group -- as it contains critical file systems such as /, /usr, /var and /tmp. rootvg can also be used for paging space and system dump devices, as well as user file systems, so it's helpful to give it some head room. You may just need the extra disk space one day.
Check Existing rootvg Size
You can see how much disk space you have in rootvg using lsvg.
# lsvg rootvg
VOLUME GROUP: rootvg VG IDENTIFIER: 00cb07a400004c000000013459f26c5e
VG STATE: active PP SIZE: 32 megabyte(s)
VG PERMISSION: read/write TOTAL PPs: 639 (20448 megabytes)
MAX LVs: 256 FREE PPs: 98 (3136 megabytes)
LVs: 11 USED PPs: 541 (17312 megabytes)
OPEN LVs: 10 QUORUM: 2 (Enabled)
TOTAL PVs: 1 VG DESCRIPTORS: 2
STALE PVs: 0 STALE PPs: 0
ACTIVE PVs: 1 AUTO ON: yes
MAX PPs per VG: 32512
MAX PPs per PV: 1016 MAX PVs: 32
LTG size (Dynamic): 256 kilobyte(s) AUTO SYNC: no
HOT SPARE: no BB POLICY: non-relocatable
PV RESTRICTION: none
In the right hand column, the TOTAL PPs (Physical Partitions) shows the rootvg is 20448 megabytes. The FREE PPs show there is 3136 mb free space.
There is a good case for keeping rootvg fairly lean, and placing user file systems in other volume groups such as datavg. See the article in the resources section below for more details.
For the purpose of this demonstration, rootvg will be increased to a total of 30 GB.
Show Disk Size with getconf
You could always add a second disk to rootvg with the extendvg command, but with virtualized storage you should be able to increase the size of an existing disk instead of adding a new one.
Before expanding the disk at the SAN layer, you can check the current disk size on the AIX logical partition using the getconf command:
# getconf DISK_SIZE /dev/hdisk0
20480
The disk size is shown in megabytes. Note that the getconf command requires the fully qualified path of the disk (/dev/hdisk0).
Grow the Disk
In this example, a SAN Volume Controller VDisk was expanded from 20 GB to 30 GB. The method of expanding a LUN will depend on your SAN configuration. For information on how to increase other types of virtual SCSI capacity, see the resources section below.
After expanding the disk on the storage subsystem, the getconf command should report the new disk size.
getconf DISK_SIZE /dev/hdisk0
30720
The disk has increased from 20480 mb to 30720 mb. However, the lsvg command still shows the same output as before. The new size has to be recognized by the AIX Logical Volume Manager (LVM). To get AIX to examine the disks in rootvg to see if any of them have grown, use the chvg command with the -g flag followed by the volume group name:
The command was successful. It did not produce any output.
Now, lsvg reports that there is a total of 30688 megabytes in rootvg, with plenty of FREE PPs (13376 megabytes):
# lsvg rootvg
VOLUME GROUP: rootvg VG IDENTIFIER: 00cb07a400004c000000013459f26c5e
VG STATE: active PP SIZE: 32 megabyte(s)
VG PERMISSION: read/write TOTAL PPs: 959 (30688 megabytes)
MAX LVs: 256 FREE PPs: 418 (13376 megabytes)
LVs: 11 USED PPs: 541 (17312 megabytes)
OPEN LVs: 10 QUORUM: 2 (Enabled)
TOTAL PVs: 1 VG DESCRIPTORS: 2
STALE PVs: 0 STALE PPs: 0
ACTIVE PVs: 1 AUTO ON: yes
MAX PPs per VG: 32512
MAX PPs per PV: 1016 MAX PVs: 32
LTG size (Dynamic): 256 kilobyte(s) AUTO SYNC: no
HOT SPARE: no BB POLICY: non-relocatable
PV RESTRICTION: none
This additional disk space can be used for expanding existing file systems, adding new ones, increasing paging space or extending the size of dump devices.
It's always helpful to give yourself enough head room in rootvg, and for most configurations it's easy to increase its disk space on the fly.
Resources
Give rootvg the space it needs: why your Operating System needs space and how to provide it
http://www.ibm.com/developerworks/aix/library/au-rootvg/index.html?ca=drs-
Growing disks in rootvg on AIX is supported from AIX V6.1 TL3 (6100-03-00).
https://www-304.ibm.com/support/docview.wss?uid=isg3T1012509
AIX 7.1 Command documentation
http://publib.boulder.ibm.com/infocenter/aix/v7r1/topic/com.ibm.aix.doc/doc/base/aixinformation.htm
Increasing virtual SCSI device capacity
http://publib.boulder.ibm.com/infocenter/powersys/v3r1m5/index.jsp?topic=/p7hb1/iphb1adddevcap.htm
Anthony English is an AIX / Power Systems engineer working in Sydney. Follow him on Twitter @AIXDownUnder.