Extension of Striped Logical Volume/Filesystem

[Cliff Lim Kok Hwee]

Hi Forum,

Currently, I have a striped logical volume lvolA of size 560GB.

/dev/vgA/lvolA
570949632 356086768 213184280 63% /mnt/sapdata1

It is striped across 4 harddisks (each of size 70GB) initially and then extended to another 4 harddisks (each of size 70GB)

#vgdisplay -v /dev/vgA
--- Volume groups ---
VG Name /dev/vgA
VG Write Access read/write
VG Status available, exclusive
Max LV 255
Cur LV 1
Open LV 1
Max PV 16
Cur PV 8
Act PV 8
Max PE per PV 2178
VGDA 16
PE Size (Mbytes) 32
Total PE 17424
Alloc PE 17424
Free PE 0
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

#lvdisplay -v /dev/vgA/lvolA
LV Name /dev/vgA/lvolA
VG Name /dev/vgA
LV Permission read/write
LV Status available/syncd
Mirror copies 0
Consistency Recovery MWC
Schedule striped
LV Size (Mbytes) 557568
Current LE 17424
Allocated PE 17424
Stripes 4
Stripe Size (Kbytes) 8
Bad block NONE
Allocation strict
IO Timeout (Seconds) default

Query: I will need to increase the striped /dev/vgA/lvolA by 100GB. But since it is striped multiples of 4 harddisks. I am proposing to have 4 harddisks each of size 25GB (instead of existing pvs of size 70GB) and then perform a lvextend using the following command
Assuming these are the 4 new pvs:
/dev/dsk/c15t1d4
/dev/dsk/c13t1d5
/dev/dsk/c15t1d6
/dev/dsk/c13t1d7

#lvextend –L 675840 /dev/vgA/lvolA

My understanding is the striping will be taken care automatically?

I do not think I will need to specify the new 4 harddisk device names?

Thanks/cliff

[RAC_1]

You are right. Add four disks and extend/create lvol.

[Muthukumar_5]

Refer this:

LVM striped logical volumes are always allocated using a strict
allocation policy. Consequently, striped logical volumes may only be
extended by a number extents that is a multiple of disks the logical
volume is striped across. For example, for a logical volume striped
across 3 disks, the logical volume will be extended in increments of 3
extents, with each of the 3 extents allocated on a different disk in
the volume group.

The pvg_name argument is allowed only if one of the allocation
policies of the logical volume is PVG-strict.

Give volume group of the logical volume also.

hth.

[GGA]

hello

vgcfgbackup the vg
pvcreate for the new disks /dev/rdsk/ ....
vgextend -g vgA vgA /dev/dsk/.... all for disks
lvextend
extend the filesystem

thats it

[Devender Khatana]

Hi,

This seems to be fine. The only precaution you should take apart from ones in normal LVOLs, while extending stripped LOVL should be that all the LUNs/Disks shall be of equal size to avaiod storage wastage.

The steps shall be
#pvcreate /dev/rdsk/c15t1d4
Repeat for other three LUNs.
#vgextend /dev/vgA /dev/dsk/c15t1d4 /dev/dsk/c13t1d5 /dev/dsk/c15t1d6 /dev/dsk/c13t1d7

As the existing policy for allocation is stripped, it will be taken in account when extending and extend will not be allowed unless atlease the no. of disks equal to no. of stripes is available i.e. 4.

Extend File system online if you have online JFS using fsadm command or do it offline after unmounting using extendfs.

HTH,
Devender

[Cliff Lim Kok Hwee]

Hi Forumers,

As mentioned, I will be extending the existing volume group vgA with smaller harddisks of size 25GB.

I do not think it will be of any issue right?

Thanks/cliff

[A. Clay Stephenson]

Yes, LVM doesn't care how big the LUN's are but in your case all 4 of the new LUN's must be the same size or space will be wasted. As long as the new LUN's are all the same size and are no bigger in capacity than the largest LUN's in the VG, you will be fine.