topic LV mirroring and how it works... in Operating System - HP-UX

LV mirroring and how it works...

Coolmar — Tue, 06 Jun 2006 12:13:16 GMT

I need to migrate data from one san to another san. I have decided to use the lvextend -m to do so. I am trying to figure out (in advance) approx. how long it will take. My question is that when I mirror a logical volume, is the mirroring of the *whole* lv and data, or just lv? In other words, would it take the same time to mirror the lv irregardless of how much data is in the lv; or there is x amount of time to mirror the LV and then x amount of time to mirror the data within the lv?

Thanks,
S.

Re: LV mirroring and how it works...

James R. Ferguson — Tue, 06 Jun 2006 12:21:53 GMT

Hi Sally:

LVM mirroring is done at the *logical volume* level and is physical extent based. That is, each LVM extent is copied to create a mirror. The filesystem and any data in it, is an abstraction layer *above* the logical volume and matters not.

Regards!

...JRF...

Re: LV mirroring and how it works...

Mridul Shrivastava — Tue, 06 Jun 2006 12:23:33 GMT

No this will take only x time to mirror data/lv, so its not 2x time only x will be taken while extending lv or syncing.

Re: LV mirroring and how it works...

Mustafa Gulercan — Tue, 06 Jun 2006 12:27:36 GMT

hi;

lvextend ,require the installation of the optional HP MirrorDisk/UX software, which is not included in the standard HP-UX operating system.
to check mirrorDisk/ux;

#swlist -l fileset|grep -i mirror

you can use lvextend like following;

#lvextend -m /dev/vg00/lvol1 /dev/dsk/c2t1d0

A mirror copy contains the same data as the original.mirror_copies can have the value 1 or 2.
The synchronization process can be time consuming, depending on hardware characteristics and the amount of data.

regards;
mustafa

Re: LV mirroring and how it works...

A. Clay Stephenson — Tue, 06 Jun 2006 12:36:03 GMT

The synchronization time depends solely upon the number of logical extents that comprise the LVOL (assuming identical hardware and system loads). LVM doesn't have a clue (or care) that a given LVOL is used as a raw device or houses a fully-cooked filesystem. All other things being equal, the time will be a linear function of the size of the LVOL.

Re: LV mirroring and how it works...

Thomas J. Harrold — Wed, 07 Jun 2006 07:50:18 GMT

Sally,

If you don't have your target disk ready yet, you can try running dd to get timings. It may not be perfect, but will get you a respectable estimate:

dd if=/dev/vgxx/lvoly of=/dev/null bs=

-tjh

Re: LV mirroring and how it works...

Coolmar — Wed, 07 Jun 2006 07:52:38 GMT

Thanks folks!