Identifying the Mirror Disk

[Karl_]

Hi all,

I have a volume group (VG03) that is stored in external disk with RAID 5 configuration.(dev/dsk/c4t0d0)

One of its logical volume (lvol7) shows that it is being mirrored. When I check using lvdisplay -v & SAM, it only displays the device dev/dsk/c4t0d0 as the disk being used by lvol7.

How can I identify which disk does the mirror copy is stored? Below is the output of lvdisplay.

========================================
LV Name /dev/vg03/lvol7
VG Name /dev/vg03
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 10000
Current LE 1250
Allocated PE 2500
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation non-strict
IO Timeout (Seconds) default

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c4t0d0 1250 2500
========================================

Thanks in advanced.

Karl

[Lee Tae-kyung]

Hi Karl,^^

The output of lvdisplay is not general.

Can I have the output of 'strings /etc/lvmtag'?

Thanks^^

[Steven E. Protter]

Based on what you've posted, /dev/vg03/lvol7 is not being mirrored

lvdisplay -v /dev/vg03/lvol7

Should show two disks if you they are being mirrrored raid 1.

I see no evidence that this logical volume is being mirrored.

Mirroring using mirror/ux is going to show two disks, /dev/dsk/c4t0d0 and another one.

Don't see that.

SEP

[Ranjith_5]

Hi

Normally lvdisplay -v gives an output which shows the PVs included in it as shown below

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c8t6d0 50 50
/dev/dsk/c0t6d0 50 50

from the above output you can find out the mirror copy.
In your case as you said it is not showing that mirroring is completed. You can the status once the mirroring is over.

Regards,
Syam

[Karl_]

Hi Lee,

The output of strings /etc/lvmtab only shows 1 disk assigned to vg03.

Hi Steve & Tyam,

Only LVs lvol7 & lvol5 shows that it is being mirrored. The other LVs don't have a 1 value in their "Mirror Copies" field.

The output of lvdisplay shows that lvol7 is mirrored (please refer to the "mirror copies" field below, under LV Status.) Attached also is the SAM screenshot.


========================================
# lvdisplay -v /dev/vg03/lvol7 |more
--- Logical volumes ---
LV Name /dev/vg03/lvol7
VG Name /dev/vg03
LV Permission read/write
LV Status available/syncd
Mirror copies 1
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 10000
Current LE 1250
Allocated PE 2500
Stripes 0
Stripe Size (Kbytes) 0
Bad block on
Allocation non-strict
IO Timeout (Seconds) default

--- Distribution of logical volume ---
PV Name LE on PV PE on PV
/dev/dsk/c4t0d0 1250 2500
========================================

[A. Clay Stephenson · Accepted solution]

This makes perfect sense. The answer to where are mirror extents is /dev/dsk/c4t0d0. You are running a non-strict allocation policy. This means that
physical extents that belong to the same LVOL can be allocated on the same physical volume or physical volume group.

This is a dangerous mode because the loss of a single PV can result in the loss on an entire LVOL. Moreover, because the I/O is occurring on the same disk for both mirrors, performance suffers as well especially during writes.

[Lee Tae-kyung]

Hi Karl,^^

Actually, while I had worked as HP engineer for 3 years in korea, I have never seen the situation.

I think it is happened by the external disk.

Is it hp product ?^^

I wonder what the external disk is.

I don't think it is reasonable.

I am sorry not to be good at english.^___^


Good day^^

[Karl_]

Hi Clay,

My guess is the same as your findings. The mirror of lvol7 is written on the same pv. I find it strange why the HP engineer that configured the external disks and the file system did not warn our IT staff in india on the risk involved.

Hi Lee,

Yup. its an hp machine (rp5470). The external disk system is a HP 2300. The server have a raid controler card.

Thanks.

Karl

[Sridhar Bhaskarla]

Hi Karl,

Post the complete output of 'lvdisplay -v /dev/vg03/lvol7'. I believe the mirror copy is also on the same disk. As you can see the "current LE" on c4t0d0 is 1250 and the number of PEs on the same disk is twice the LEs due to mirroring.

In the 'lvdisplay -v /dev/vg03/lvol7' you will see both PV1 and PV2 as c4t0d0 itself.

Having mirror on the same disk will help very little. Moreover, it can impact the performance terribly as the system has to write onto the same disk twice for a single operation.

-Sri

[Sridhar Bhaskarla]

Karl - Forget my last post.. It took sometime before my response got posted...You already got the answer. 0 points for both these posts please.

-Sri