Midrange SANs with high-end features from Compellent, Xiotech

As high-end storage systems come out with new features, those features tend to migrate down over time to systems intended for the smaller enterprise. Two midrange SANs, Compellent’s Storage Center 3.3 and Xiotech’s Magnitude 3D 3000e, are taking advantage of this, offering a wealth of features that as recently as six months ago were limited to much more expensive systems.

The list of these previously high-end capabilities includes multiple tiers of storage (15,000-rpm Fibre Channel, 10,000-rpm FC, SATA), migration of data from one tier to another, the capability to migrate data from a RAID10 FC volume to a RAID5 SATA volume without interrupting access to the data, and the capability to expand existing volumes without reformatting. Given the rapid growth of data in most enterprises and the order-of-magnitude difference between high-end SCSI or FC drives and SATA-based storage, these features -- especially multiple tiers of storage in one system -- give administrators much-needed flexibility.

The products are comparable in price and features, although Compellent has an edge in performance and maturity -- what takes a dozen steps with the Xiotech system can be accomplished in a couple of steps with the Compellent system. It’s not that the Xiotech system won’t do what the Compellent box will do; it’s just that it’s more complicated.

Compellent Storage Center 3.3
To test these systems, I attached them to Windows and Linux hosts, created volumes and mapped them to specific hosts, created replicas of the initial volumes, expanded the volumes beyond their initial size, migrated volumes from first- to second-tier storage, and ran IOmeter performance tests.

The Compellent Storage Center consists of a storage controller and one or more drive shelves. The drive shelf accommodates 16 SCSI U320 or ATA drives. Setting up the system was as simple as installing the drives in the drive shelf, powering on, and connecting to the browser-based interface.

Compellent’s administrative interface is clean and easy to navigate, showing a level of maturity that Xiotech can’t quite match. Creating volumes is straightforward, and all tasks you might need to perform are readily accessible and well documented through the help system. A topology view allows you to see a logical map of the SAN and to click and drag to connect servers to volumes; a folder view allows assigning management of specific server/volumes to specific users.

Many of the setup tasks are automated, so administrators who haven’t been specifically trained on storage administration will find them less daunting. Wizards make initial setup straightforward. Just as simple to perform are tasks such as setting up replication or data migration.

The automated data migration is an excellent example of Compellent’s streamlining work. There are three tiers of storage available: RAID10 on high-performance drives, RAID5 on high-performance drives and SATA drives. You can define a high-performance partition as tier one or two, and a SATA partition as tier three.

Next, if you have the optional Data Progression software installed, data is migrated from the highest-performance tier to the lowest during a period of 12 days. This migration happens automatically, based on whether the data has recently been accessed and how often. Data Progression can be enabled on a per-volume basis, but it is not based on additional rules -- it’s either on or off for the whole volume and uses as many tiers of storage as are available.