Until now I've been mirroring the drives in my luns for maximum redundancy. I have a new installation of VI3 coming up and redundancy isn't the goal, maximum storage is. There is 7.2 TB in raw disk available, is it okay to divide this into 2TB LUNs for ESX using RAID 6 (2 drive fails tolerated) or even RAID 5 to maximize the storage I have available to me?
What would be the reasons for not wanting to do this? What does everyone else do?
I would go with RAID 5. It will give you some good speed and some redundancy as well. RAID 10 is the perfect balance of speed and redundancy, but you will loose half your space! I have a SAN with multiple LUNS over iSCSI configured with RAID 5 using SAS 15K drives and its blazing fast. The performance is outstanding!
If maximizing storage is the goal then Raid 0 is actually your best option. :smileyblush: The main thing to think about is what are giving up when you change? Redundancy with Raid6 protects you from a two disk failure but it has a higher I/O penalty on writes since the parity is calculated twice. Most of the cacluations go like this:
Raid Level I/O overhead
Raid0 (Reads+Writes) = total I/O Overhead
Raid 1 (Reads + 2 X Writes) = total I/O Overhead
Raid 5 (Reads + 4 X Writes) = total I/O Overhead
Raid 6 or ADG Or whatever (Reads = 6 X Writes) = total I/O overhead.
So with Raid 5 and 6 you usually give a little performance back but gain additioanal storage capacity. Many times that write overhead can mitigated by write cache on the storage array.
Just like any other times, it's depends At this time the most important think is the underlying disk system.
If you are using SATA or FATA with big (>250 GB) drives then I definetely suggest to use RAID 6 (or dual parity).
If you are using reasonably sized FC drives (<300 GB & 15k) then the most cost efficiently and operationately
choice is RAID5 with 400-500GB LUNs. And if you have plenty of rooms in your storage system and also cash
then the RAID1 (or RAID10) is not a bad option.