INetU Labs takes on the Dell MD3000i: Is it an Enterprise-capable workgroup SAN?

September 2nd, 2009 by Andy B.

Recently INetU Labs put Dell’s low cost workgroup SAN through its paces to see how it compares to the more robust (and costly) Equallogic and EMC offerings. The results are in, and it seems that correctly configured, the MD3000i is great product with plenty of bang for your buck.

Configuration

For testing we used an MD3000i populated with a mix of 146GB SAS and 500GB SATA drives. The SAN shipped with a single controller but a second was added to test failover. A word of warning here – Dell configures the duplex mode based on how the SAN is ordered; if you add a second controller later you’ll need to use the command line tool to enable it, a process that’s not stated as a clear requirement and takes a little digging on the Internet to find documentation for. That being said, once you find the docs you’ll have it set in no time. Our test unit was a major firmware revision behind, and bringing it up to date took a good twenty minutes. Minor revision updates probably won’t take as long, but this is something to keep in mind if you’re striving for multiple nines of availability.

Once the hardware was configured and updated, the software install was a snap. The management software is somewhat cumbersome but gets the job done, and configuring the LUNs is a simple process. We were testing multipath (MPIO), and Dell requires a specific version of the iSCSI initiator on Windows servers, so be careful here, too. Fortunately, the supplied driver CD made sure the right version was installed.

Benchmarking

For the testing process, we connected the MD3000i’s redundant controllers to a dedicated gigabit switch (two connections per controller) and ran two more connections back to each server (Dell 2950’s). Of course, in production we would use a pair of switches, but a single switch is fine for a lab. Using some industry standard software (iozone), we ran multiple passes across the LUNs and found the performance to be respectable. Some tweaking of settings in the switch (Jumbo Frames) and the iSCSI initiator yielded improvements. MPIO functions adequately with path failover occurring pretty quickly (though this was something we tweaked away from Dell’s recommended values). Controller failover is also handled well with no loss of data, with delays that Windows Server 2003 was able to handle.

General performance of the unit was good, and definitely impressive for its price point.

Conclusion

The MD3000i is a great workgroup SAN with a place in mid-level clusters, such as moderately sized database or file servers. Support for Windows and Linux is good, but be sure to read the documentation carefully, and be prepared to tweak the configuration to maximize performance. We found that multiple passes were needed to get the most out of the device.

An interesting feature we encountered was the use of network bandwidth. With two paths available to the disk, each would run at slightly less than 500Mbps. If one of the paths was disabled, the other would jump to almost a full 1Gbps. Dell technical support was unable to explain this behavior, and it doesn’t seem to be a limitation of the switch, server, or (in Dell’s opinion) the MD3000i backplane. Testing on Red Hat Linux yielded the same behavior so it’s also not a driver issue. Either way, being unable to use more than 1Gbps when up to 2Gbps is available is a slightly frustrating feature. Dell’s Equallogic line does support port aggregation to ‘bond’ multiple GigE ports for maximum bandwidth, but this is a more expensive unit.