LVM and VxVM

LV mirroring and how it works...

 
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Coolmar
Esteemed Contributor

LV mirroring and how it works...

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.
6 REPLIES 6
James R. Ferguson
Acclaimed Contributor
Solution

Re: LV mirroring and how it works...

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...
Mridul Shrivastava
Honored Contributor

Re: LV mirroring and how it works...

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.
Time has a wonderful way of weeding out the trivial
Mustafa Gulercan
Respected Contributor

Re: LV mirroring and how it works...

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
A. Clay Stephenson
Acclaimed Contributor

Re: LV mirroring and how it works...

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.
If it ain't broke, I can fix that.
Thomas J. Harrold
Trusted Contributor

Re: LV mirroring and how it works...

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
I learn something new everyday. (usually because I break something new everyday)
Coolmar
Esteemed Contributor

Re: LV mirroring and how it works...

Thanks folks!