Disk mirroring - removing the original PV?

[David Griffiths]

Good evening,

I should know this, but I need to ask to be sure.

OK, here's the scenario:

Volume group 'VG_A' is made up of a number of external EMC san PV's ('SAN A'). The logical volumes are then mirrored to another set of external EMC san PV's ('SAN B').

The server on which VG_A is defined is then moved to another site, and is physically connected to SAN B. We no longer require the mirroring of the logical volumes within VG_A, but specifically want to retain the mirror PV's within 'SAN B' and remove the 'SAN A' PV's from VG_A.

In essence I want to remove the original PV's (SAN A) from VG A and keep the mirror PV's within VG A (SAN B).

Is this possible?

The reason for this is that, for an application specific reason, we could not use EMC SRDF to allow data copy & migration - so HP-UX OS mirroring was used.

Many Thanks,

Andrew Austin.

[Patrick Wallek]

Just 'lvreduce' the mirrors and specify the /dev/dsk/c?t?d? path to the PV's on SAN A.

[Pedro Cirne · Accepted solution]

Hi,

I had a very similar cenario one month ago.

If I understood you are physically moving the server where the VG_A is and connecting the HBAs to another physical SAN Switch and you just want to keep the "side" of the mirror that is in SAN_B.

For this you have 3 main steps:

1-Before moving the server, reduce the mirror you have on SAN_A. You can do this using lvreduce on all lvols:

lvreduce -m 0 /dev/VG_A/lvols [followed by the complete list of the PVs on SAN_A]

2-Also before moving the server, you must remove the PVs of SAN_A from VG_A, using vgreduce:

vgreduce VG_A [all the PVs of SAN_A, including alternate links if you have them]

At this point on /etc/lvmtab you have VG_A defined only with PVs from SAN_B, without mirror.

Now you must ask EMC if the disks that the server will "see" on the new physicall location will have the same IDs, I mean the same /dev/dsk/c#t#d# they have on present location. If this is true you just have to connect the server on the new physicall location and turn it on!

BUT, IF THIS NOT TRUE, you must vgexport VG_A to a mapfile (-s -m) before moving the server and then vgimport VG_A when the server is connected to the SAN on the new location, check man pages for information on vgexport/vgimport, I don't have acess to a hp-ux server at this moment to give you the correct syntax.

Enjoy :)

[generic_1]

So I take it you are doing LVM mirroring instead of BCVs right?

[David Griffiths]

Thanks to both of you for the reply.

Pedro,

To be honest, I pretty much had the whole thing down, the only part I was unsure about was being able to specify the original PV's within VG_A.

We have been moving a lot of kit and re-attaching to 'SAN B' recently, and as we were never sure if the /dev/dsk/****** devices would change, we have routinely exported & imported each of the affected VG's on each server as a 'catch all'. We will probably do the same on this one.

Finally, for your information, the only kit we have left to move are IBM pSeries servers running AIX 5.2 / 5.2. The procedure is far more straight forward in attaching to a different SAN.

Thanks again, points will be assigned.

Andrew Austin.