What configuration yields the best performance?

[henno]

We have 24-drive Supermicro server with 24 600GB 10k SAS drives, connected to MegaRAID SAS controller with BBU. We want to set ip up for 2 ESXi 5.1 servers as a datastore through ISCSI or NFS. We don't need the storage space but rather the performance.

What would be more desired way of setting things up:
a) Creating eleven 2-drive RAID1s in megaraid and letting FreeNAS to create something from these virtual drives. What RAID or other configuration would give the best performance here?
b) Creating one big 22-drive RAID10 in megaraid with 2 drives for hot spare and presenting that to FreeNAS.

?

- - - Updated - - -

We could also add up to four Intel X25-e SLC 1gen SSD drives to that server, if that would be beneficial any way to the array (ZIL, L2ARC). We could add them directly to the motherboard but there is no hardware raid then. Can Freenas stripe them and use the result as cache?

 

[henno]

Option b) seems to give the possibility to reinstall operating system without worrying about the data array.

- - - Updated - - -

I think that my basic question is that is there any performance benefit when giving FreeNAS all the disks vs letting the controller do RAID10.

 

[tingo]

There might not be performance benefits, but there might be benefits related to reliability. zfs really likes to have direct access to the drives, with as little as possible "in between".

 

[henno]

There might not be performance benefits, but there might be benefits related to reliability. zfs really likes to have direct access to the drives, with as little as possible "in between".

Could you give an example of reliability benefits of not having anything "in between"? What happens when system (OS) drive crashes?

Henno

 

[tingo]

Which system drive? The FreeNAS one? Nothing bad happens - you install FreeNAS on a new usb stick, boot up, restore config (you have made a backup of the config of course) and you are back in business again.
If you haven't backed up your config, you will need to import your zfs volume and configured your FreeNAS again before you are up and running.

As for reliability benefits of having zfs as close to the "metal" (drives) as possible, let's your your "option b)". What happens if the raid setup on the drives from the raid controller get's screwed up? Well, as far as zfs knows, you have one big drive, and two spares. Hardly a reliable setup for a raid pool. Result - your'e screwed unless you have a backup.