Any risk with running chvg -t on live system

[rodak]

I need to add a 300GB volume to a volume group. extendvg tells me I
need to increase the number of PPs per PV using chvg -t. What bothers
me is that the message says to use the command to "attempt to change"
this value. Researching it, it looks like that wording is there
because there are some situations where it might not be possible, but
I figured I'd ask here first. This is an AIX 5.3 system, the PVs are
LUNs presented from an EMC SAN.

Is there any risk to running this command?

vg stats below:

VOLUME GROUP: vg04 VG IDENTIFIER:
00c086be00004c00000
0010728e50569
VG STATE: active PP SIZE: 256
megabyte(s)
VG PERMISSION: read/write TOTAL PPs: 958
(245248 megabyt
es)
MAX LVs: 256 FREE PPs: 96 (24576
megabytes
)
LVs: 5 USED PPs: 862
(220672 megabyt
es)
OPEN LVs: 5 QUORUM: 2
(Enabled)
TOTAL PVs: 2 VG DESCRIPTORS:
3
STALE PVs: 0 STALE PPs:
0
ACTIVE PVs: 2 AUTO ON:
yes
MAX PPs per VG:
32512
MAX PPs per PV: 1016 MAX PVs:
32
LTG size (Dynamic): 1024 kilobyte(s) AUTO SYNC:
no
HOT SPARE: no BB POLICY:
relocatable

[Hajo Ehlers]

On Nov 4, 10:31 pm, rodak <robert.macn...@gmail.com> wrote:
> I need to add a 300GB volume to a volume group. extendvg tells me I
> need to increase the number of PPs per PV using chvg -t. What bothers
> me is that the message says to use the command to "attempt to change"
> this value. Researching it, it looks like that wording is there
> because there are some situations where it might not be possible, but
> I figured I'd ask here first. This is an AIX 5.3 system, the PVs are
> LUNs presented from an EMC SAN.

The -t option will cut down the maximum amount of disk per vg. In case
it does not matter for you on the long run ...
Thus MAX PVs: 32 will be go down to 16 ,

But the point is: MAX PPs per PV: is 1016

Thus in case you add a disk in size of less then 262656 MBytes ( >=
MaxPPs 1016 * PP Size 256 MB ) you do not have to use the -t at all.

Another option is to change to a big volume group.

hth
Hajo

[Uli Link]

Hajo Ehlers schrieb:

Not relevant in most cases today:
You cannot importvg volume groups with more than 1016 PP per PV into AIX
earlier 4.3.2.
But most hardware used today won't even boot with those obsolete releases.

--
ULi

[rodak]

Thanks for the responses. I ran the command, did it's job, was able
to add the 300GB volume. No problems.

[Niel Lambrechts]

On 2009-11-04 23:31:07 +0200, rodak <robert....@gmail.com> said:

> I need to add a 300GB volume to a volume group. extendvg tells me I
> need to increase the number of PPs per PV using chvg -t. What bothers
> me is that the message says to use the command to "attempt to change"
> this value. Researching it, it looks like that wording is there
> because there are some situations where it might not be possible, but
> I figured I'd ask here first. This is an AIX 5.3 system, the PVs are
> LUNs presented from an EMC SAN.
>
> Is there any risk to running this command?

I've seen it crash a server where the VG had paging on it, it
presumably locked the VG for this be an issue. Not sure if this
scenario is still relevant in current versions though.

Personally, I would have done this in a maintenance window if paging is
involved.

Regards,
Niel