A Different Way to Add More Space to ASM DiskGroup in a Linux/RAC Environment

Usually when you need to add more space to an ASM DiskGroup, you add more disks of same size to the DiskGroup. Here is a different way to accomplish the same goal, it sounds a little scary at first but it actually works. In a RAC environment with EMC SAN as storage, we have a DiskGroup A that contains one LUN of 100GB. To increase the size of this DiskGroup to 200GB, you can create a LUN of 200GB, in Navisphere, then migrate the existing 100GB LUN to this larger LUN. This migration process can run in the background and be invisible to OS/Oracle/End users. After the migration is done, you get a larger LUN/Disk in DiskGroup A, however, to make ASM "see" the extra 100GB, two more things will need to happen:

1. Make OS recognize the extra space. Before the LUN migration, there was one partition of 100GB on that LUN, after the migration, the partition is still 100GB even though the LUN is 200GB. Re-partition is needed to make OS aware of the added extra space on the LUN. Unfortunately, fdisk doesn't provide a method to extend the partition, which leads to the scary part: the original partition has to be deleted, and a new partition is then created to take all of the LUN space. As long as you make the start of data the same as the old partition, no data will be lost. In our case, ASM sits on top of raw device without ASMLib, so the re-partition process can be done online without downtime.
   

   
    

2. Make ASM recognize the extra space. After step 1, OS recognizes the extra space, but ASM still doesn't. You can verify it by running the following query:
   
   select name, total_mb, free_mb from v$asm_diskgroup;
   
   To make ASM recognize the extra space, you'll need to run:
   
   alter diskgroup {diskgroup name} resize all rebalance power 11;
   
   Now verify it again with the first query, you'll see that ASM now "sees" all the space from that LUN.