topic Re: Mirror/UX: Does the order in which the pv are specified matter? in Operating System - HP-UX

Mirror/UX: Does the order in which the pv are specified matter?

Romaric Guilloud — Wed, 19 Oct 2005 01:24:48 GMT

Hello there,
I'm running a vg that uses Mirror/UX.
The mirrored LE are on a remote site.
Local LUNs are c29tYdZ and remote LUNs are c21tYdZ.
At lvdisplay, I see that the first PV of a given LE is the "remote" one, and the second PV of this LE is the "local":

miller4 >lvdisplay -v /dev/n4r5vg01/lvol4 |more
--- Logical volumes ---
LV Name /dev/n4r5vg01/lvol4
VG Name /dev/n4r5vg01
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 200
Current LE 25
Allocated PE 50
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation strict
IO Timeout (Seconds) default

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c29t7d0 25 25
/dev/dsk/c21t1d0 25 25

--- Logical extents ---
LE PV1 PE1 Status 1 PV2 PE2 Status 2
00000 /dev/dsk/c21t1d0 00033 current /dev/dsk/c29t7d0 00058 current
00001 /dev/dsk/c21t1d0 00034 current /dev/dsk/c29t7d0 00059 current
00002 /dev/dsk/c21t1d0 00035 current /dev/dsk/c29t7d0 00060 current

Is there a performance issue there?
I.e does the order in which the PVs are specified matter in the performance of Mirror/UX.

Indeed here, I was wandering if it was not silly to write the "primary" I/O remotely, then to carry the mirroring on the local PV.

If Mirror UX is fully synchronous, then my remark might not apply...

Thanks for any advice/comment in the matter.

Regards.

Romaric.

Re: Mirror/UX: Does the order in which the pv are specified matter?

RAC_1 — Wed, 19 Oct 2005 01:40:32 GMT

/stand swap and root has to be in the same order as that of primary disk. Others need not be. Else system won't boot.

Re: Mirror/UX: Does the order in which the pv are specified matter?

VIKAS AGRAWAL — Wed, 19 Oct 2005 02:02:26 GMT

order is required only for boot disk , for data disks it does not required any specific order .

your above output seems no error

If u r setisfied then give points & close the issue

Re: Mirror/UX: Does the order in which the pv are specified matter?

Romaric Guilloud — Wed, 19 Oct 2005 02:05:20 GMT

RAC, I'm afraid you did not read my question.

Re: Mirror/UX: Does the order in which the pv are specified matter?

Bharat Katkar — Wed, 19 Oct 2005 02:36:28 GMT

Hi,
Are you sure that c29tYdZ and c21tYdZ are remote to each other?

If so there is definitely going to be performance problem.

Normally mirrors are done on local sites.

Regards,

Re: Mirror/UX: Does the order in which the pv are specified matter?

Romaric Guilloud — Wed, 19 Oct 2005 02:56:44 GMT

Bharat, it's a campus cluster!
That's why c21 is remote.
Got it?

Re: Mirror/UX: Does the order in which the pv are specified matter?

RAC_1 — Wed, 19 Oct 2005 03:36:38 GMT

I would certanly want local to be first copy. this would save you on bandwidth.

Re: Mirror/UX: Does the order in which the pv are specified matter?

Bharat Katkar — Wed, 19 Oct 2005 03:58:28 GMT

I got it!!
Now what RAC says make sense.
Regards,

Re: Mirror/UX: Does the order in which the pv are specified matter?

SGUX — Thu, 20 Oct 2005 01:42:59 GMT

it should not matter because the mirrors are supposed to be equal. There is no such thing as 1st and 2nd. What probally would happen is that the I/O's come from the "local-disks' because they respond faster then the "remote-disks"

Re: Mirror/UX: Does the order in which the pv are specified matter?

Romaric Guilloud — Thu, 20 Oct 2005 04:12:00 GMT

Thanks Francois, very pertinent answer.
I did guess there were no notion of first/second pv in such a config.
Rgds,