It is very hard to find fault with the Dot Hill R/Evo 2722. It's a solid step into the smaller 2.5-inch form factor, with an easy-to-use GUI, extremely strong performance and a high-availability architecture.
The Dot Hill 2722 is a 2U RAID storage array that can house as many as 24 2.5-inch drives accessible via dual 4Gb Fibre Channel controllers. By using 2.5-inch drives (which are 70 percent smaller than 3.5-inch drives), data centers can pack more high-performance storage into a smaller space, use less electricity, and generate less heat and vibration.
According to Seagate, a 2.5-inch drive can consume up to 50 percent less power than an equivalent 3.5-inch drive. As the price of high-performance 2.5-inch drives decreases, expect to see more enterprise storage products shift to this form factor.
Built on the same core architecture as the Dot Hill 2000 series product family, the 2722 can support additional drive enclosures connected via SAS to scale up to 96 drives. The unit I tested had dual RAID controllers, each with Fibre Channel, RS-232, Ethernet and external SAS connections.
For performance and redundancy, each drive has dual SAS ports, with one connected to each controller, and cache is simultaneously mirrored between controllers. In addition, each controller cleverly avoids the use of battery-based cache backup with four super capacitors and integrated Compact Flash storage. The system also includes dual hot-swappable power supplies.
Pricing for the Dot Hill R/Evo 2722 starts at less than $15,000 for a unit with 24 drives and a single controller. As configured for the review (dual controllers, fully populated with 24 36GB 15K SAS drives), the system would have a street price of about $19,000.
During tests, installation went smoothly. I installed a Qlogic QLE2562 PCI Express dual-port 8Gb FC Host Bus Adapter in my Lenovo RD120 test server. (One of the advantages of using a Qlogic HBA is the included SANsurfer management and diagnostics software.)
I then rack-mounted the 2722 and made Fibre Channel and Ethernet connections to both controllers. I was running Windows Server 2003, so I had to install the Dot Hill DSM (device-specific module) to enable Microsoft Multipath I/O; this is not necessary with Windows Server 2008, as support for MPIO is built-in.
From my server, I launched a Web browser and connected to the 2722's default IP address. I logged in using the default management user name and password.
The Web GUI, or RAIDar Storage Management Utility, is well-organized and easy to use; there is also a command-line interface.
Upon logging into the server, the first thing I saw was the System Overview, which provides information on the health and utilization of the system, enclosures, disks, vdisks, volumes, snap pools and snapshots.
Across the top of the frame are menus for View, Provisioning, Configuration, Tools and Wizard; this meant that any task I needed to accomplish was never more than two clicks away.
By clicking on Physical, Enclosure 0 in the Configuration View frame on the left side of the browser, I was able to see a graphical representation of the unit itself, with drive, controller, power supply and interface status indicated in the proper place. Clicking on a specific drive makes its light flash, which made it very easy to find my way around both the GUI and physical unit itself.
I ran the Provisioning Wizard, which walked me through creating a RAID set (or virtual disk) by selecting RAID type (the 2722 supports 0, 1, 3, 5, 6, 10 and 50), providing a name, associating with a controller and selecting which physical drives should be in the RAID set.
Next, I initialized the vdisk, a task that can be performed online (for immediate use) or offline (for use after complete initializations). I then created a volume, performed mapping, and established read and write privileges.
A comprehensive context-sensitive help system guided me through everything. Most people will have no trouble at all installing a storage array of this class, but terminology varies from vendor to vendor, so it never hurts to have good help when you need to clarify something.
There are two primary ways of configuring snapshots: AssuredSnap and AssuredCopy.
AssuredSnap provides the 2722 with built-in volume snapshot capability and performs SCW (single copy on write) operations on snapshot data to utilize disk space more efficiently. Taking this further, AssuredCopy creates a full volume copy (versus a logical volume copy with AssuredSnap) to protect against virtual disk failure and eliminate application I/O bottlenecks.
To assess performance, I ran Iometer 2006.07.27 to generate a number of different workloads representative of a database/e-commerce environment, a mail server environment, a streaming media environment and combinations of these environments.
Throughput was consistently in the range of 350MB ps to 800MB ps, with average latency in the 2- to 15-ms range. Performance peaked during the streaming media workload, with a 3.37-ms average response time at a pretty stellar 998MB-ps total throughput. You'll note that this throughput exceeds 4G-bps Fibre Channel, but it's per controller. By running half the Iometer load against Controller A and half against Controller B, I was able to run some massive workloads.
Matthew D. Sarrel is executive director of Sarrel Group, an IT test lab and editorial services and consulting firm in New York.