[CentOS] How does LVM decide which Physical Volume to write to?

Sat Sep 19 08:58:39 UTC 2009
Fabian Arrotin <fabian.arrotin at arrfab.net>

Oliver Ransom wrote:
> Hi everyone.
> 
> This isn't specifically a CentOS question, since it could apply for  
> any distro but I hope someone can answer it anyway.
> 
> I took the following steps but was puzzled by the outcome of the test  
> at the end:
> 
> 1. Create a RAID1 array called md3 with two 750GB drives
> 2. Create a RAID1 array called md9 with two 500GB drives
> 3. Initialise md3 then md9 as physical volumes (pvcreate)
> 4. Create a new volume group called "3ware" with md3 (helps me  
> remember what controller the disks are on)
> 5. Use vgextend and add md9 to the 3ware volume group.
> 6. Add a logical volume filling the volume group then create a ext3  
> filesystem on the entire volume.
> 
> Now I started moving a lot of data onto the volume and iostat said all  
> the data was being written to md9. Why that array? How does it decide  
> which physical volume to write to?
> 
> I could not find any documentation or information online about how  
> exactly this works.
> 

What ? no documentation covering LVM admin on/for CentOS ? hmm, is 
http://www.centos.org/docs/5/html/5.2/Cluster_Logical_Volume_Manager/ 
not reachable from your side ?
How have you configured you LV ? linear or stripped ?
-- 
--
Fabian Arrotin
idea=`grep -i clue /dev/brain`
test -z "$idea" && echo "sorry, init 6 in progress" || sh ./answer.sh