Maximum number of hard disk within a volume group.

[JI HUI]

System: HP K380
OS: HP-UX 11i
HP-UX 10.20

Question:
If there any limitation in HP-UX in term of how many hard disks could be put under one volume group?

We have one system where 12 hard disks were configured in one volume group and configured in one logical volume. We noticed that one hard disk is showing "NO_HW" when we run ioscan -FnCdisk. And our supplier claimed that we should have maximum 4 in one logical volume.

Is it true? Need your advice.

Thank you.

[Jeff Schussele · Accepted solution]

Hi,

The maximum number of disks is 255.

This value is set with -p XXX in the vgcreate command.
Default value is 16.

Your supplier is incorrect, it's dependent upon needs. There is no reason why LVs should be limited to max 4 drives, none at all.

The NO_HW indicates a problem with that disk, it should be checked for proper install & functionality. Could be a bad disk.

HTH,
Jeff

[S.K. Chan]

If you take a look at the man pages for vgcreate, the -p option allows you to define the max number of disks allowable in a volume group during its creation. If you don't specify anything the max is 16 disks (ie the default). Seeing "NO_HW" in ioscan has nothing to do with LVM. The disk might be having some kind of hardware problem or it might be a "stale" device. Do you get anything back when you run diskinfo on it ?

[Denver Osborn]

The maximum number of physical volumes in a volume group can be set at 255. The default value is 16. You can view the current Volume Groups limit with vgdisplay, look for the "MAX PV" entry.

vgdisplay /dev/vg_name


For the disk in ioscan showing "NO_HW", you may want to check into that further. If no hardware was removed from the running system, then you've possibly got a failed disk.

Hope this helps,
-denver

[T G Manikandan]

The default value of maximum disks in a VG is 16.

THe maximum is 255.

you can specify that using the -p option of vgcreate.

NO_HW should be some other problem relating to the disk.

[JI HUI]

Thank you all for your fast response.

the max PV showed in vgdisplay is 16. So it should be already for us to have 12 hard disks.

Secondly, I believe that there should not be any connection between number of hard disk with LOGICAL volume. Number of hard disk is controlled by volume group itself. Correct me if I am wrong.

Third, very sadly, our supplier in this case, is HP in the country.

thank you.

[Michael Tully]

There is no connection between the number of disks in your volume group and that of the logical volume itself. You can utilise the entire number of disks in your volume group from 1-255 if you wished. (This would used in a striping situation)
As stated the default number of 16 is made upon the creation of the volume group if no number is specified. You can have up to 255 disks if the PE is not exceeded.

[Denver Osborn]

Then maybe there must have been a misunderstanding somewhere... how are your lvols setup that could possibly limit the lvol to span only 4 disks??

do you have 2 mirrored copies?
is there any type of raid?

-denver

[T G Manikandan]

The default value of maximum disks in a VG is 16.
THe maximum is 255.

you can specify that using the -p option of vgcreate.

NO_HW the hardware at this address is no
longer responding

try replacing the drive.
The last option can be checked by rebooting the system

[S.K. Chan]

You are right .. there should not be any connection between number of hard disk with LOGICAL volume. A logical volume can span across multiple disks depending on how it was created earlier and extended later. Once you got all your disks into the volume group, it's like a big pool of physical extents for you to start allocating them in your logical volume.