Cache SSD's or use them directly for iSCSI

[invisiblade]

I'm working on setting up a FreeNas box to serve iSCSI targets to an ESXi host, but I'm not exactly sure the best way to configure the storage.

HardDrives:
2 256 GB SSD's
4 2TB WD Green Drives (Yes... I know. I will replace them soonish).
10 GB Ram (Might be able to increase).

For my ESXi host, I have 5-10 low usage VM's running at one time, and one VM that has a decent amount of IOPS hosting a Postgres DB and running a lot of php scripts all day.

My question is, what would give me better performance from FreeNas while still being redundant?

I'm fairly sure I'm going to put the Green's into a RAID 10. But what about the SSD's?
Here's the options I'm thinking of:

1. Use one for Log, one for Cache, for the RAID 10.
2. Use one for my high IOPS VM directly.. Split the 2nd SSD into 2 partitions, one for cache and one for log for the RAID 10. (Technically the Freenas is on the ESXi host, so it's really simple to split drives using two vmdk's).
3. Use a smaller portion of the SSD's for Log/Cache, and put the VM's on the SSD's, and only use the RAID 10 for storage for the VM's.

Any input is appreciated.

 

[jgreco]

You'd be likely to find the SSD's in mirrored mode to make for an enjoyable and responsive datastore. They'd probably be much more functional in that purpose than they would as L2ARC/ZIL,

 

[invisiblade]

Thanks for your input. I tested it, and you're right, the throughput for the RAID 10 with the cache/log isn't all that great compared to using the SSD's as the datastore.