How to grow a hardware Raid 5?
I couldn't disagree with joeqwerty more to be honest. You don't mention which controller you have but all of the PERC 5 and 6 cards can perform live array expansion, although I'd be strongly tempted to fully backup your volume first. This way your new drive/s will become part of the R5 array and so will be able to survive a single disk failure. If you simply add another extent then in the event of losing a disk you stand a good chance of losing the whole VMFS datastore (the risk lessening if you're on ESX/i v4), plus expanding the array to 6 drives gives you 300GB more space than two 3 drive arrays.
The simplest thing to do might be to create a new RAID5 array and add it to the VM datastore as a new extent.
To anyone else looking at this:
On the older PERC 5 cards you could just pop the drives in and run a reconstruction in the RAID BIOS to add capacity or do a Raid Level Migration (RLM)
On the PERC 6 you'll need to install the Open Manage Server Administrator. It takes a few extra steps when installing on ESXi, but it's worth it. You can expand a live array without any interruption in service. Although be aware that it does take a looooonnnnnggg time to rebuild the array after adding a drive (plan 4-6 hours at least), and during the rebuild you'll have degraded service.
- Shut down all hosts and install OMSA, then enable CIM using the steps outlined -> OMSA install on ESXi
- Then in order to access OMSA install the Managed Node Admin Tool on a separate station. (Can’t just use htps://server:1311)