Help with L2ARC in Nexenta CE

[agrikk]

I'm setting up a Nexenta CE iSCSI-based SAN for use in a SQL Server lab and I'm wondering:
- how much cache I'll need
-how to determine the L2ARC / ZIL cache usage
- if having SSDs allocated for L2ARC / ZIL is actually helping or not

I currently have eight SATA-2 (3.0gbps) disks in a single volume of mirrored pairs totalling 2.3TB of space, with a pair of Samsung 256GB 840 PRO SSDs on a M1015 controller (cross-flashed to LSI9211-IR) for L2ARC. I had the drives available so I tossed them into the mix, but I'm wondering how much good they are doing/will do and if I need both in there.

This filer will be the shared iSCSI storage for a SQL Server 2012 cluster running about a half dozen small databases, but the largest of which is pushing 150GB and billions of records. The database is updated hourly, which adds about 2 million rows at a time (consisting of 1.5 million user numbers and their scores at that time). Data access is mostly sequential in nature (tracking users scores over time).

Since the filer will mostly be getting hit with sequential database usage patterns, will 512GB of L2ARC be overkill? How do I know what to look for, performance-wise?

The hardware is:
Supermicro H8SGL-F motherboard
8-core 6128 Opteron @ 2GHz
16GB RAM
M1015/LSI9211-IR controller with 2x 256GB Samsung 840 Pro SSD
HP P410 controller with 512MB BBU Cache with 8x WD Blue 640GB SATA-2 drives

 

[bmh.01]

More ram if you can. The l2arc pointer table is held in ram so you use more ram for the bigger l2arc you have.

If the write is mostly sequential you may get away without a slog device.

I have a love/hate thing with nexentastor but it does seem improved with v3.1.5.

 

[agrikk]

I have a love/hate thing with nexentastor but it does seem improved with v3.1.5.

I understand what you mean. I've been messing with it for a week or so now and I keep having to fight the urge to go back to my trusty Openfiler when I hit "WTF Nexenta?" moment.


I have very little funds available for this project, but maybe I'll sell one of the SSDs and pick up more RAM. It looks like I have a long haul of benchmarking in my future.