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

[Romaric Guilloud]

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.

[RAC_1]

/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.

[VIKAS AGRAWAL]

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

[Romaric Guilloud]

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

[Bharat Katkar]

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,

[Romaric Guilloud]

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

[RAC_1]

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

[Bharat Katkar]

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

[SGUX · Accepted solution]

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"

[Romaric Guilloud]

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