topic Re: VG extension in Operating System - HP-UX

VG extension

jeevanandham — Tue, 15 Sep 2009 10:42:35 GMT

Hi Team,
I have a doubt in vgextension,

I have done a vg extension in one of our hpux server which is in production environment.
activity is extending a filesystem from 10GB to 15 GB (increasing 5GB )of particular filesystem

i have 639 PE in a VG Each PE= 16 MB

639x16=10224 MB

i need to extend 5GB (5120 mb)

so 10224+5120 = 15344 mb

when i execute
lvextend -L 15344 /dev/vgname/lvname

it throws error as

lvextend: Not enough free physical extents available.
Logical volume "/dev/vgsappbi/lvsappbi" could not be extended.
Failure possibly caused by strict allocation policy

then i executed

lvextend -L 15328 /dev/vgname/lvname

it extended successfully

what happened to 15344 -15328 = 16 MB (1 PE)
can any one clear my doubt ? how its happened
Please....

Re: VG extension

Robert-Jan Goossens — Tue, 15 Sep 2009 10:56:50 GMT

Hi,

Could you post the output of

# vgdisplay -v vg_name
# lvdisplay -v /dev/vg_name/lv_name

Regards,
Robert-Jan

Re: VG extension

Hakki Aydin Ucar — Tue, 15 Sep 2009 11:00:24 GMT

You have probably run out of your device belong to Hard Disk. You can see this by issuing:

lvdisplay -v /dev/vgname/lvname

Re: VG extension

jeevanandham — Tue, 15 Sep 2009 11:10:20 GMT

Ya i agree that its out of space availability,

the thing is when it alloted 10GB the available PE was only 639 =10224,
10GB =10240-10224 =16 here also i missing 1PE

and when i extend 5GB 5120MB

that is 10+5 =15GB
10240+5120 =15360MB

But here is

10224 +5104 =15328 MB

each time 1 PE is losing

LV availability is only 639 when it was 10 GB

Re: VG extension

jeevanandham — Tue, 15 Sep 2009 11:21:10 GMT

This is when the file system was 10GB (before extending to 15 GB)
#
# vgdisplay -v /dev/vgsappbi
--- Volume groups ---
VG Name /dev/vgsappbi
VG Write Access read/write
VG Status available
Max LV 255
Cur LV 1
Open LV 1
Max PV 50
Cur PV 1
Act PV 1
Max PE per PV 1016
VGDA 2
PE Size (Mbytes) 16
Total PE 639
Alloc PE 639
Free PE 0
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

--- Logical volumes ---
LV Name /dev/vgsappbi/lvsappbi
LV Status available/syncd
LV Size (Mbytes) 10224
Current LE 639
Allocated PE 639
Used PV 1

--- Physical volumes ---
PV Name /dev/dsk/c4t1d6
PV Name /dev/dsk/c6t1d6 Alternate Link
PV Name /dev/dsk/c8t1d6 Alternate Link
PV Name /dev/dsk/c10t1d6 Alternate Link
PV Status available
Total PE 639
Free PE 0
Autoswitch On

Re: VG extension

Hakki Aydin Ucar — Tue, 15 Sep 2009 11:52:06 GMT

So from your opinion, (I am not sure just thinking) system does not give all free bytes as it holds 1 PE for some reasons such as some LV data backup or something ..

Re: VG extension

jeevanandham — Tue, 15 Sep 2009 11:55:51 GMT

Ya me too think that system holds 1 PE for some precaution purpose, but i need to confirm this...

Did anybody have any idea about this and help me out

Thanks in advance......

Re: VG extension

Hakki Aydin Ucar — Tue, 15 Sep 2009 12:26:35 GMT

Check:

pvdisplay /dev/dsk/cXtXd0 to see if you still can see free PE ?

Re: VG extension

Hakki Aydin Ucar — Tue, 15 Sep 2009 12:34:12 GMT

And besides note that:

if you cannot see your disk cXtXdX with command

# pvdisplay /dev/dsk/cXtXdX

issue the command:

# vgdisplay -v |grep "PV Name" to see if your disk is in the list, if not it is not a member of LVM Group.

Re: VG extension

jeevanandham — Tue, 15 Sep 2009 12:47:34 GMT

i think those commands will not help me to know about the missing PE.. because in availability PE itself its not showing the full size... my question is why its taking one PE in hide but when i increase by 1PE its extending without any cross cut.

Re: VG extension

R.K. # — Thu, 17 Sep 2009 09:54:06 GMT

Hi Jeev,

ANOTHER question rises, is that, why your vgdisplay was showing "Free PE" as zero, BEFORE extending.

Total PE 639 <<===
Alloc PE 639
Free PE 0 <<===

And still you can extend the LV?

Re: VG extension

jeevanandham — Thu, 17 Sep 2009 10:54:02 GMT

Let me clear that the out put was when filesystem was 10 GB before assining 5 GB LUN
*******************************************
when is assigned 10 GB
(10 GB =10240 MB) right

i will get 10240 MB (1024x10)

if 1 PE =16 MB

i should get 640 available PE right?

but i am getting only 639 PE

that is

639x16 = 10224 MB

10240 - 10224 = 16MB = 1PE ?
******************************************

Re: VG extension

Ishwar_1 — Fri, 18 Sep 2009 10:52:53 GMT

When LVM allocates disk space to a logical volume, it automatically creates a mapping of the logical extents to physical extents.

This mapping depends on the policy chosen when creating the logical volume.

For example,
1>If its Logical Volume is normal then it will be mapped to 1 Physicla Extent only
2>If one mirror copy exists, then each logical extent maps to two physical extents, one extent for the original and one for the mirror copy.