Volume Group and Physical Volume

[Cliff Lim Kok Hwee]

Gd Day Forum,

Currently I have a volume group vg05 as follows:

# vgdisplay vg05
--- Volume groups ---
VG Name /dev/vg05
VG Write Access read/write
VG Status available
Max LV 255
Cur LV 2
Open LV 2
Max PV 16
Cur PV 3
Act PV 3
Max PE per PV 1023
VGDA 6
PE Size (Mbytes) 4
Total PE 3069
Alloc PE 3000
Free PE 69
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

It consists of 3 x 4092MB harddisks and they are LV striped between them.

Query: I would like to add in 3 harddisks each of size > 4092MB. Is it possible? I don't think I am able to bcos the "Max PE per PV" is already set to 1023 and the PE size is set to 4MB.

Query: Is it non-advisable to have different sizes of PV in a particular Volume Group?

Thanks/cliff

[bhavin asokan · Accepted solution]

see the max PE option with vgcreate command.


-e max_pe Set the maximum number of physical extents
that can be allocated from any of the
physical volumes in the volume group. The
default value for max_pe is 1016. However,
if the size of any physical volume exceeds
1016 times the pe_size, the default value for
max_pe is adjusted to match the physical
volume size. The maximum number of physical
extents can be a value in the range 1 to
65535.



you can add up to 16 hdd in this vg group.
maximum size you can get from one pv is 1023*4=4092MB (man PE extents*one extend size.)
max size you can get for this vg is 4092*16=65472MB.(max size from one disk*max number of PVs.)

max PE per PV in your case means that you can't use more than 4GB from one PV even the disk is more than 4GB .

regds

[Sunil Sharma_1]

Yes. You can add hard disk having PE more then 1-23 but you will be able to use only 1023 PE.
It's wastage of Disk space so create new VG and use these disks.

There is no issue haveing different size of PV in same VG. It's mostly depend how you will create volumes and how you use them ?

Sunil

[Michael Tully]

If you are adding 3 x 4092 disks (each one will use 1023 extents each) based on 4mb extents, that is fine.
The extent size is per disk. Just be aware that 1023 extents is the most you will be able to have per volume. If you tried to add a larger disk like 18Gb, you would only be able to use 4092Mb of it.

[bhavin asokan]

you can have different size PVs in the same logical volume.the 'max PE per PV' is set to higher numbers if you want to use bigger size hdds.

once created you will not be able to change this value in normal cases without destruction of VG . For increasing this value you should have to take the ignite backup of total vg ,remove the vg and recreate the vg with -e max_pe option (a higher number )and then restore the ignite backup.

regds,

[Prashant Zanwar_4]

Hi,
There are no issues at all as you said you will be using 4092MB disk. If we calculate logically 4092/4=1023 will be total Physical extents you can have on your disk. So the disk is getting nicely utilized. Your Max PV is set to 16 which means you can have 16 disks of 1023*4 size. Even if you use higher capacity disks, that wont help you much as you will be wasting space.
If you select higher capacity disks, create a new volume instead.
I remember, there are some problem with using HP-PB dirves with the Wide SCSI dirves. I guess you are not mixing them anyhow.
Hope it helps

Thanks
Prashant