lv mirror !!!

[Anand_Sree]

I have a logical volume which had 10 disks. I had to move this LV to another SAN and so I allocated 10 disks from the other san but unfortunately, Because of the VG characteristics, I can only have a max of 16 disks. I ended by migrating data from 5 disks. But with this approach, Performance was so bad that I had to stop it. Now My question is can I mirror the PE on a particular PV to another PV and then break the mirror ? .

--- Logical volumes ---
LV Name                     /dev/vg05/lvol1
VG Name                     /dev/vg05
LV Permission               read/write  
LV Status                   available/syncd          
Mirror copies               0           
Consistency Recovery        MWC                
Schedule                    parallel    
LV Size (Mbytes)            68000          
Current LE                  17000    
Allocated PE                17000      
Stripes                     0      
Stripe Size (Kbytes)        0                  
Bad block                   off         
Allocation                  strict                   
IO Timeout (Seconds)        default            

   --- Distribution of logical volume ---
   PV Name            LE on PV  PE on PV 
   /dev/dsk/c19t3d0   2157      2157     
   /dev/dsk/c19t3d1   2157      2157     
   /dev/dsk/c19t3d4   1280      1280     
   /dev/dsk/c19t3d5   1280      1280     
   /dev/dsk/c19t3d6   1097      1097     
   /dev/dsk/c27t2d7   2129      2129     
   /dev/dsk/c27t3d0   2129      2129     
   /dev/dsk/c27t3d1   2129      2129     
   /dev/dsk/c27t3d2   2130      2130     
   /dev/dsk/c27t3d3   512       512      

The c19 is all old disks currently in use and c27 is all new disks which are from the new san. The goal is to remove the remaining 5 disks from c19 . Thanks for any input .

[James R. Ferguson]

Hi:

With 'lvextend' you can specify a partiular physical volume as the target for a mirror as long as the allocation policies ('strict') are observed.  After all, you never want mirror copies on the same physical disk.  See the 'lvextend' manpages for more information.

I have done many SAN-to-SAN migrations by mirroring from the old to the new SAN and then reducing the mirror from the old when done.  This works very well.

If LVM geometry (e.g. 'max_pv') is a concern, look at 'vgmodify' to change that.

Mirror operations do degrade performance somewhat, but it only hurts for a little while :-)

Regards!

...JRF...