Dell Compellent – A brief introduction

I don’t really do product evaluations on this blog for a few reasons. Firstly, I’m not a tech journalist, and don’t get sent review samples of equipment to look at all day, nor do I get paid to do product evaluations (generally speaking). Secondly, I’m a bit crap at hardware evaluations, and tend to approach these things with a set of requirements that don’t always match up with what other people find useful in evaluating kit. In my day job, however, I sometimes have the opportunity to look at kit, but usually during the evaluation stage there can be a bit of problem with commercial sensitivity and me shooting my mouth off about Vendor X’s gear while negotiating the purchase of said gear. That said, I’ve been evaluating some Dell Compellent equipment at work lately and thought it might be worthy of a write-up or two. Please note that I’m not suggesting for a minute that you go out and spend yours or someone else’s cash on Compellent arrays without doing your own evaluation. The point of this post is more to talk about some of the things I like and dislike, based on the opportunity I’ve had to have some hands-on experience with it.

For a decent, if now slightly out-dated, review of the Compellent, check out Chris Evans’ reviews here and here. For Dell’s overview of the Dell Compellent Architecture, have a look here. Also worth looking at is the Compellent Software Overview, which can be found here. Finally, a cool feature is “Portable Volume”, you can read about that here.

It was installed in early February and hasn’t really missed a beat. The system came with 2 SC8000 controllers with 64GB of cache each.  We also got 2 trays of disk; one with 24 300GB 15K SAS drives and one with 12 2TB 7.2K NL-SAS drives. Each controller has one 4-port 8Gb FC front-end card and one 4-port 6Gb SAS back-end card installed. It came with the basic Storage Center software licenses, Data Progression licenses and a Virtual Ports Base license.

Here’re some pictures of it installed in the rack in our lab. Note that these pictures probably don’t look too different from a lot of other Compellent arrays installed in racks around the world. They do, however, prove that the person installing the gear was competent.

IMG_5169

IMG_5168

So, I thought I’d cover off briefly on a few things now, and if anything else comes to mind I’ll do some more posts.

Firstly, Virtual Port technology is kind of cool, once you get your head around it. Basically, NPIV (check out one Scott Lowe’s very useful articles on NPIV here) is used to enable multiple virtual ports on a physical port. Dell suggest that this means you need less ports for failover. While this is true, keep in mind that there may well be bandwidth issues when ports do failover. Obviously, you’d be hoping that the local Dell support technician turned up to replace failed cards in a timely fashion. Still, the idea of not having to worry as much about jumpy host-based failover software is neat (I’m looking at you, older versions of EMC PowerPath). I’m going to do a brief article on virtual ports in the future. In the meantime, this is what it looks like from a zoning perspective:

fcalias name Compellent1_Virtual_Ports_Zone vsan 2
    member pwwn 50:00:d3:10:00:58:70:05
    member pwwn 50:00:d3:10:00:58:70:07
    member pwwn 50:00:d3:10:00:58:70:19
    member pwwn 50:00:d3:10:00:58:70:1b
fcalias name Compellent1_Physical_Ports_Zone vsan 2
    member pwwn 50:00:d3:10:00:58:70:2d
    member pwwn 50:00:d3:10:00:58:70:2f
    member pwwn 50:00:d3:10:00:58:70:31
    member pwwn 50:00:d3:10:00:58:70:33
zone name HOST-023_HBA0_Compellent1_Zone vsan 2
    member fcalias HOST-023_HBA0
    member fcalias Compellent1_Virtual_Ports_Zone
zone name HOST-024_HBA0_Compellent1_Zone vsan 2
    member fcalias HOST-024_HBA0
    member fcalias Compellent1_Virtual_Ports_Zone

And the same again for VSAN 3, obviously with different host HBAs and different physical and virtual ports.

Secondly, note that LUNs / volumes on the Compellent are always configured as thin. You can choose not to do this, but you’ll have Dell people scratching their heads and wondering what you’re doing. People in the street might call you a disk hugger, or worse. It can get nasty. Let’s just say that thin is the new thick. If you absolutely have to configure thick, you used to be able to do so by ticking a box when you configured the volume. I made a 20TB volume that way. Sales people were briefly excited until they realised it was an evaluation array. For the life of me I can’t see where to do that, maybe it was removed as an option.

While you’re thinking about how you might have just wasted a bit of money on advanced Compellent features by insisting on configuring thick-provisioned volumes, you can do some benchmarks. The great thing about benchmarks is that you can have them do whatever you want them to do. We asked for a system that could deliver approximately 10000 IOPS. And that’s what we got. I’m going to do a longer article on synthetic benchmarks and how they can be useful, but let’s just say that if you’re sitting down to do an equipment evaluation and you’ve fired up IOmeter (or whatever you like to use), make sure you have an idea of what it is you want to prove before you click on start. We also were able to get a lot more IOPS out of the system, because 512b 100% sequential reads are pretty common, right? Here’s a picture that represents two volumes running 2 workers with IOmeter. Each worker was doing 70000 IOPS. OMG that’s over 140000 IOPS! Yeah. Which equals approximately 70 MBps for this particular benchmark. It’s been said before, but don’t forget that an IOPS figure in isolation is meaningless.

140000_IOPS

I’m not in the business of shilling for Dell. But sometimes I get to look at their stuff. If you like the sound of some of this stuff, and think you might be in the market for a new array, it might be worth giving them a call.

3 Comments

  1. Pingback: penguinpunk.net » Dell Compellent – Preallocating storage

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