On Sept. 10, Dell added a new iSCSI storage array to its portfolio: the PowerVault MD3000i — a fully redundant enclosure that can pack dual power supplies, dual RAID controllers and 15 SAS (serial attached SCSI) drives in 2U. Two expansion modules can bring the overall capacity to 45 drives, which, by year’s end should also include SATA drives. At rollout, the MD3000i supports SAS drives only.
If the name of the array sounds familiar, it’s because this is the iSCSI version of a modular enclosure with SAS connectivity by the same name: the MD3000. As a sweeping generalization, think of the MD3000i as the same hardware with different controllers.
Dell appropriately positions the MD3000i as a step up from the SATA-only AX150/i and as a more affordable option than the entry-level Clariion models. Each controller of the unit carries dual Gigabit Ethernet and a separate management port, which in full configuration offers the choice between the combined transfer rate of four iSCSI connections and the resilience of active fail-over.
For my evaluation I received an MD3000i with two controllers and fifteen 73GB, 15K RPM SAS drives. My test unit also had Disk Copy and Snapshots, two optional features that make it possible to take as many as 128 snapshots and make 255 systemwide disk copies.
Starting with wizards
Setting up the array didn’t take long. I connected each GigE port to one of my four servers. Next, I connected the two management ports to a separate subnet. While powering on, the array automatically acquired an IP address for its management ports.
To manage the array, you install the MDSM (Modular Disk Storage Manager) application on at least one machine. From this application you can do major management activities such as configuring the array, provisioning storage, and monitoring hardware. All those tasks are easy to find by opening the GUI’s well-organized tabs.
After a quick install, I instructed MDSM to automatically discover the array. In a few seconds the array was found and under control. Next, I assigned IP addresses consistent with my SAN to its four data ports and set them to use jumbo frames for better performance.
To help you become productive quickly, the MDSM has numerous wizards that make configuration choices with little human intervention. For example, choosing automatic configuration will create four virtual disks assigning a hot spare but let you choose the RAID level from 0,1,3, or 5 . Assign each of the virtual disks to its host and you are ready to go.
Smart features with some exceptions
The MDSM GUI, while helpful, doesn’tcover all the possible administrative tasks. Some activities, such as recovering from some intricate error conditions, are available only via CLI, but the GUI simplifies command-line tasks with a Recovery Guru wizard that suggests clear steps to guide the admin’s actions. During my evaluation I had to type commands only twice and both times the Recovery Guru passed me a cheat sheet.
Another smart feature of MDSM is the ability to easily switch from in-band to off-band management, which obviously gives administrators the flexibility to start the GUI from wherever it’s most convenient.
Assigning each virtual disk to one of my application servers was easier than it usually is with iSCSI. The array comes with a host agent that simplifies linking each iSCSI initiator to its target. After installing each agent, MDSM automatically discovered the new host and left me to make the connection to the appropriate virtual disk. As an additional bonus, from MDSM you can easily keep an eye on the storage used by each server.
Dell suggests that you can connect as many as 16 hosts to the MD3000i, but don’t expect top performance concurrently on all of them. After running a few benchmarks simulating I/O-intensive transactional access from my four application servers, I was convinced that the array can take more. However, the four GigE connections could become the bottleneck if you run numerous concurrent, data-intensive jobs such as backups.
One thing I didn’t like: MDSM doesn’t have load-monitoring applets. However, the array keeps cumulative statistics of the traffic on each iSCSI port that help in spotting a persistent load unbalance. Another annoyance: the appliance serializes some operations if they are logically dependent. For example, while creating a snapshot for a virtual disk, a message stopped me because there were not enough physical drives in the storage group. I added the drives, but still couldn’t create the snapshot until the previous operation, often a long one, completed. To be accurate, the GUI lets you continue immediately if you accept creating the snapshot in a different disk group, but it would be preferable to let the admin schedule the job anyway and put it in a queue until the previous one is finished. By contrast, it’s difficult to find anything wrong with the resilience characteristics of the MD3000i. After pulling out a drive, removing one of the controllers and one of the power supply modules, my test job was still running.
If your servers and your network are properly equipped, that host agent also brings multi-path capabilities. Moreover, the array has 1GB of mirrored, battery protected cache that helps to boost performance and shelters data from sudden power shut-offs.
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