Improve Performance for 500GB+ iSCSI Files?

[mevans336]

We have a re-purposed Dell R610 which unfortunately, only has 32GB of RAM. It has 2 x LSI SAS 6Gbps cards, connected to 2 x Dell MD1220 arrays. The arrays hold a mix of SSD and SATA drives. I have 2 x 10Gbps ports into this server, 2 x 1Gbps for management.

I have a zpool stripe which consists of 4 zdevs that are 4 x 1TB WD Red drives in a RAIDZ1.

This device is an iSCSI VMware target, used for SQL backups. So we're sending single files once a night of 500GB+, then every 15 minutes smaller files, of a few hundred MB to a few GB. The nightly 500GB+ backups is read by another server to refresh its data. The full 500GB from the latest file is read every night.

I am only seeing a 17% ARC hit rate and I'm seeing a 0.0 hit rate for everything else like demand_data and demand_metadata.

I have recently been gifted 4 x 1TB SSD drives that I would like to utilize in some manner to improve backup and restore speeds for the 500GB+ nightly backups.

First - is this even possible? I could probably enable synchronous iSCSI for writes and set an SSD as an SLOG, but I can max out a 10Gbps link currently so I don't see the benefit there. I think the biggest benefit would be to cache the latest backup to an SSD via L2ARC somehow, but again, I don't think this is possible with FreeNAS.

Any suggestions - I'm open to experimentation also, as we back this data up elsewhere, so failure of this FreeNAS box is acceptable.

 

[Stux]

Well, you could make a new SSD pool out of the 4x 1TB SSDs. You could even then replicate that pool to your spinning disk pool for extra safety.

How you structured that is up to you, for example, 4-way RaidZ1 would get you circa 3TB of SSD storage, and probably able to saturate 10gbe. Whereas mirrors would only result in 2TB, but better performance.

With the replication to spinning rust strategy, you could keep minimal snapshots on the ssd pool, and more snapshots on the hd pool.

Theoretically, if you had enough RAM you could use one of the 1TB SSDs as L2ARC, and that'd help a lot, but you don't have enough RAM to maintain a 1TB l2arc.