VTRAK Performance

churnd · JBOD Joined: 14 Nov 2009 Posts: 3

I also have several older stype Apple RAIDs and a new Active Storage XRAID, which I have been using to compare to the VTRAK. The older Apple RAIDs are configured RAID5 with 512k stripe, and the Active XRAID is dual RAID6 configured for general I/O (not sure about stripe width). We recently purchased a VTRAK E610f 16TB SATA for additional storage.

I"ve configured the VTRAK as one large RAID6 LUN with a hot spare with a 64k stripe and using Apple's recommended settings for the controller options as per their HT1200 KB under "Manual Config". Settings for the LUN are Read Policy: Read Ahead... Write Policy: Write Back. This server is only a file server, using SMB and AFP. All testing was done locally on the server.

While I understand this config doesn't fall under Apple's recommended configurations for optimal performance, I'm getting throughput results that are very low, and I feel they could be better.

I originally started off with the above configuration, was not happy with the results, reconfigured using Apple's dual RAID5 with two hot spares config. My results were slightly better, but still nothing to get excited about.

Now, I suspect it's the 64k stripe width, but I notice that all of Apple's configuration scripts use that setting, and if you set up the LUN manually using the Express setting with the "File Server" option, it defaults to the 64k setting. I assume 64k is some kind of magic number with this particular hardware?

The only other info I've been able to obtain from searching around is someone said they got better throughput from disabling "Adaptive Writeback Cache" (AWC). From what I understand, the AWC is enabled to prevent data loss during a power outage IF the controller batteries are being reconditioned. Our DC has multiple power backup UPS systems, so losing power isn't really something I'm concerned about. Is it safe to leave this disabled? Should I change the LUN settings to WriteThru?

The only benchmark I've been using is Xbench to compare results. Several tests on the RAID6 LUN yielded similar results:

Adaptive Writeback Cache Disabled

JesusAli · Xsan Master Joined: 25 Jul 2008 Posts: 151

Hmm... the situations are so different, I don't even know if comparing the numbers makes any sense, but here are my results, regardless:

churnd · JBOD Joined: 14 Nov 2009 Posts: 3

JesusAli · Xsan Master Joined: 25 Jul 2008 Posts: 151

churnd, how are you connecting your VTRAK E-Unit to your Client computers?

churnd · JBOD Joined: 14 Nov 2009 Posts: 3

VTRAK is plugged in directly to the Apple 4GB Quad FC card in my Xserve. Xserve is a file server on my LAN.

I know it's not an XSAN setup, but I hoped I'd still get help from you guys anyway since you're experts in the field. Smile

JesusAli · Xsan Master Joined: 25 Jul 2008 Posts: 151

I haven't worked with the Promise as just a RAID Unit, without Xsan... but I would guess the largest utility would come from utilizing BOTH controllers in the VTRAK E-Unit.

Simultaneously spreading out a file load over the concurrent use of multiple physical disks (RAID 5 or 6) is what provides speed, so doing that simultaneously with two dedicated hardware Controllers, and two different groups of disks, sounds like the way to go.

So making 1 RAID 6 volume seems like a bottleneck because can't only 1 Controller (and subsequently, one two Fiber Ports) be in charge of any 1 Logical Disk?

So it does seem that two RAID 5's, each made from 7 Physical Disks, (leaving 2 Global Spares) would be a good idea.

But what I don't know is, can the Promise "offer up" those two RAID 5's as 1 Volume? ...or is that what you need Xsan to accomplish?

Is that what the Metadata Controllers do for Xsan, keep track of how all the LUNs are Striped together?

What about making a Disk Utility Software RAID 0 out of the two RAID 5's offered by Promise? Would the software RAID 0 be the bottle neck?