Mirroring lvol made up of multiple pv's onto a single larger pv...

[grahamswilson]

Hi...

I did find some almost relevant posts, but wanted to seek some "fresh" advice/input...

We want to move from one storage environment to another and want to use mirroring to do so - but - if you have a LV made up of a bunch of PV's...and want to mirror to a single larger PV in the process...I know this works, with a simple

lvextend -m 1 /dev/vgXX/lvolYY /dev/disk/new_large_pv.

What I'm looking for is clarification on what happens in this scenario when you break the mirror.

If the original and new PV were the same size, I would do a

lvextend -m 0 /dev/vgXX/lvolYY /dev/disk/original_pv

which would remove the original disk and leave the new disk, but, what would I do to remove the smaller, multiple PVs from the mirror, leaving only the new larger PV?!

Some of these servers are older 11iv3 and dont have lvmove, and I was hoping to use mirroring rather than pvmove.

Any input/advice welcome.

[Torsten.]

In this case you will do

lvextend -m 0 /dev/vgXX/lvolYY /dev/disk/original_pv1 /dev/disk/original_pv2 ...

[Patrick Wallek]

In this case you will do

lvextend -m 0 /dev/vgXX/lvolYY /dev/disk/original_pv1 /dev/disk/original_pv2 ...

I think you mean:

lvreduce -m 0 /dev/vgxx/lvolYY /dev/disk/original_pv1 /dev/disk/original_pv2 . . .

[grahamswilson · Accepted solution]

Fantastic!  Thank you...

Simply name all the smaller PV's on the command line during the lvreduce command!

So obvious...

...and thanks for the clarification, I did mean lvreduce not lvextend, but good catch and thanks for clarifying...

[Torsten.]

Sorry, my fault - just did a copy and paste ... :-(

[efinneran]

You don't have to be quite that explicit if you don't want to.  LVM uses the concept of copy 1 and copy 2 (and optionally 3). If you do an lvdisplay -v on the logical volume and scroll through all that output, you can see it list for each physical extent (line), which drive holds the first copy (I call it 'left column') and the second (right column).

In your case you should see al those different little drives showing up in the left column, and the new larger single physical volume in the right column.  When you do the lvremove, all you need to provide is enough information to know which copy you would like to remove versus which copy you want to keep. Provided when you specify that lvremove, that you include at least one physical drive that is on the list in the left column, that will tell LVM you want to remove the first copy and keep the second copy. As a result, it will remove all the drives listed in the left column, leaving you with a single copy on your new drive.You could list all the different drives that are present in the left column, but the result will be the same as specifying only one.

If you were really curious, you could do a subsequent lvdisplay -v and see that the extents listed in the right column (copy 2) have now moved to the left column and become copy 1 (the only copy at that point).

-- Ed