Physical Extents (mirror & pri) on same disk ???

[James Purtell]

Help experts ...
I have PE's (pri & mirror) residing on the same disk and I'm not sure if this is an optimal config.
The disk is one of four internal drives that utilize MirrorDisk/UX and contain vg00 and related lvol's.
The lvol mount point is /opt. A portion of it is on c2t3d0 and the same portions mirror is on the same disk c2t3d0.
Please see the attached file.

Thanks
Jim

[James Purtell]

Sorry about that . .
. . here's a better attachment.

[David Hixson · Accepted solution]

Jim,

The quick answer is 'oh my, you gotta do something about that, quick!'.

Mirroring to the same disk causes a number of problems. The first is that you do not gain any availability benefits at all, and probably increase your chance of having an outage because of the added complexity.

Secondly, you are going to have interesting performance problems on the parts of filesystem that reside at the end of that lvol. Reads will come from every-other extend on the disk... and I'm not sure exactly how it will queue up the writes, but it surely will not be optimal for performance.

Be aware that when you break the mirror, the lvol will remain on every-other physical extent... so you will need to re-mirror it to make it contiguous, then cut away the primary and build it back so that the PEs are sequential on both mirrors.

[James R. Ferguson]

James:

No, this is not at all desirable from a high-availability standpoint, as you would conclude. I would reduce the mirror and re-establish it with strict allocation (the default).

...JRF...