How does LVM decide which Physical Volume to write data to?

oli · 09-05-2009, 05:56 AM

I am moving data from a single drive to a new volume group called "3ware" (helps me remember which controller the drives are attached to!).

The steps I took are as follows:

1. Created a PV made of /dev/md3 (two 750GB drives in RAID1).
2. Created a PV made of /dev/md9 (two 500GB drives in RAID1).
3. Added the 750GB then the 500GB physical volumes to the new volume group (in that order).

Now when I started moving data onto the new group I can see with iostat that the data is being put onto md9. So what determines which physical volumes get the data?

gothicbob · 09-08-2009, 06:27 AM

Good question, I'd never really thought about it before so I did a little research. Wikipedia has a decent explanation of LVM, but this website which was referenced is more definitive.

http://sunoano.name/ws/public_xhtml/lvm.html

Not a direct answer to your question, but hope I've helped.