Cracking the iSCSI conundrum

Posted on 5 Mar 2010 at 17:09

Steve Cassidy battles to get his iSCSI setup working properly

I watched the man from Dell visibly relax at the end of the demonstration build we went through, and that was for several reasons. One was that I told him I was going to keep that heavy-metal backbone routing switch that he’d humped down the Northern Line to get to me, and so he’d be going home empty-handed.

Then there was the fact that the demo had worked. The justification for using a big fat Layer 3, high-powered switch had become plain as day as soon as I started firing a few gigabytes at the servers, because all the boxes that I’ve listed here – the PS4000, the T510s and the PowerConnect 6224 – have thermostatic fans, and once data started moving through the built-up system it was the switch that became hot first, giving the game away by its dust-raising whine of cooling fans.

I count that as “case closed” when it comes to choosing the place to spend your time and effort in making iSCSI work well.

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User comments

dedicated iSCSI switch

Very dramatic and enjoyable read, Mr Cassidy. Thank you!

I was more than once involved in a purchase of Dell's iSCSI storage, and i can assure everybody that Dell's sales reps will never sale you an iSCSI storage without making sure that you understand the importance of dedicated switch(es).

By stasi47 on 8 Mar 2010

+1 for dedicated switches

The first thing I thought, on page 1, when the guy was talking about iSCSI was that you need a separate switch just for the iSCSI traffic - and I'd want a decent switch as well...

It always amazes me that "experienced" networking people still fall over on the basics sometimes.

Thanks for a good read.

By big_D on 9 Mar 2010

Diagrams please

It would be rather usefull to acompany each of your stories with one or two simple digrams, I dare to suggest?

Senior TA

By dusanjovanovic on 10 Mar 2010

We don't have unlimited budgets for our IT Dept.

Dell kindly gave us two power connect 5424's for free when we pruchased our kit.

Utilising VLAN's enabled us to isolate our iSCSI traffic from our VM network, mangement network and production network.

The setup has been running for over a year and we are yet to experience any issues that you have described.

Due to the success of the iSCSI implementation we were then able to purchase a ps6000 for our live environment.

One assumes when implementing iSCSI Solutions that the team involved would be well versed in the technologies to know the potential pit fulls.

The same goes for Fibre Channel for that matter.

I'm not entirely sure of the moral of the story and can only assume it would be "Do your homework before you implement".

By lavann on 12 Mar 2010

this a conundrum?

can't say I've dealt with Dell's sales force at all, but I can't imagine they don't tell people the networking needs to be set up properly. My company has been using the EQL units for several years now, and we're up to 11 of the full arrays. It's my understanding the 4000-series is lower-end.

We're running several hundred VMs, Exchange for 1100 users, and Oracle RAC on them. We can't afford dedicated iSCSI switches yet, but we've had no issue with stacked Cisco 3750s with the iSCSI on its own VLAN and the ESX/Oracle having multiple dedicated iSCSI NICs on that VLAN.

We actually switched the Oracle RAC from Sun v880 boxes attached to Sun FC 3510 arrays, and we always had database hotspots and I/O issues with that setup. We've had none so far on the EQL. Not entirely similar setups with Oracle, which no doubt helps (ASM now vs no ASM before, etc.), but overall we've been very pleased.

Sure, I'd be thrilled with an IBM or Hitachi SAN or maybe NetApp Filers (we looked at all of them). But iSCSI was the only way we could get both the IOPS capacity and the storage space capacity we needed for the dollars we had.

We still use a slew of the inexpensive HP 12-SATA disk NAS boxes for our normal file server-type data (uncompressible medical data that consumes enormous amounts of space) because even the iSCSI is way too $$ per GB for that.

By pstd1 on 13 Mar 2010

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Steve Cassidy

Steve is a networks expert and a contributing editor to PC Pro for more years than he cares to remember. He mixes network technologies, particularly wide-area communications and thin-client computing, with human resources consultancy.