SAN storage systems continue to evolve quickly, with features trickling down from market leaders such as EMC and Hitachi Data Systems to midtier players. The three systems reviewed here, from Compellent, iQstor, and Xiotech, offer a surprising array of functionality including nearly every feature one might find in $250,000 enterprise-class systems except CAS (content addressed storage). Their impressive feature sets include 4Gbps FC (Fibre Channel) connectivity, iSCSI support, tiered storage, local and remote replication and snapshots, and even thin provisioning, boot from SAN, virtualization, and automatic expansion of volumes. Compellent even provides automatic migration of data from first- to second- or third-tier storage -- an ILM (information lifecycle management) tool that is usable without requiring a complex setup. Both Compellent and Xiotech offer monitoring and support services similar to those the tier-one storage vendors provide to large enterprises, allowing customers to respond proactively to projected failures.
[ See also: Fast guide to fancy SAN management ]
Great strides have also been made in ease of setup and administration. For instance, configuring a partition on the Compellent system to be remotely replicated on a second system hundreds of miles away was literally a two-minute job.
The three systems range in price (as tested) from $21,195 to $76,813, but with the price as configured it is difficult to make an apples-to-apples comparison. Capacity is not merely a matter of number of drives times drive capacity -- all of these systems support multiple tiers of storage, using 15K, 10K and 7.2K FC drives as well as the enormously less expensive and higher capacity (though slower and less reliable) SATA drives. Xiotech even offers an SSD (solid state disk) option that offers an extreme performance gain at a much higher cost per gigabyte -- a 6GB solid state module that fits into the same drive bays as the other disks.
System performance will greatly depend on a number of factors, including the types of drives installed, interface speeds, servers connected (operating system, drivers, HBAs installed, software in use), RAID levels of the partitions in use, number of drives in the partition, and the name of the administrator’s favorite cartoon character. Although the Xiotech system offers the ultimate in performance with SSD drives, the fact that a 6GB SSD drive is more expensive than a 750GB SATA drive will limit SSD use to the most performance-critical applications, such as database indices. Due to the varying numbers and types of drives, I did not attempt to measure performance across the systems, but instead focused on testing the features to ensure they performed as expected.
Compellent Storage Center
The Storage Center I received from Compellent came in two pieces: a Storage Center appliance and one 16-drive enclosure, which was equipped with eight 300GB 10K drives and eight 500GB 7.2K drives. The Storage Center can be used as a single controller for multiple enclosures, or dual controllers can be used for redundancy. Each enclosure supports three different classes of FC drives -- 15K, 10K, and 7.2K -- as well as SATA drives. The system as shipped came with 6.4TB of raw capacity, more than the others, and not at the highest price.
Setting up the Storage Center is a simple matter of configuring the IP address of the controller through a serial connection, which is usually performed by the Compellent tech during on-site installation. The wizards that help you automatically configure the system for use can safely be left in their default configurations, and virtually any setting you make can be changed later without having to reconfigure the volumes you create. This includes RAID levels, spare drives, number of tiers of storage, volume size, and more. The system automatically defines storage tiers based on the types of drives available; if more storage is added, additional tiers become available.
[ CompellentStorage Center 3.5 was selected for an InfoWorld Technology of the Year award. See the slideshow to view all winners in the storage category. ]
Compellent has clearly put considerable development effort into usability. Most features have setup wizards that make configuration a simple matter of entering the necessary information, or more often, selecting it from a list of available choices, and taking the default choices for most items. Thus, setting up and cloning boot from SAN configurations using the Server Instant Replay function, or setting up remote replication over IP to a second Storage Center in another location, are both simple operations. Remote replication includes deduplication and encryption, although not dedicated compression.
The automated data migration feature is unlike many ILM systems in that the administrator does not have to manually designate files to be moved or even create policies that move all files of a certain type or location. Instead, data that is infrequently accessed is moved automatically from the first-tier FC drives (10K or 15K) or second-tier FC drives (7.2K) to third-tier SATA-based storage, without requiring manual configuration or intervention by the administrator. Frequently accessed data is automatically kept in first-tier storage, and data that has been migrated is automatically moved back to first-tier when it begins to be used. Of course, the admin can designate partitions or even folders that will not be automatically migrated, if desired.
The instant replay function is another extremely useful feature of the Storage Center. An instant replay is a snapshot of the system at a given point in time. Because an instant replay uses only pointers to data, two replays use only as much storage as is required to store the pointers and copies of any files that have changed between the two snapshots. This amounts to data deduplication, and allows for virtually unlimited snapshots (unlimited by the software and limited physically only by disk capacity). Instant replay also supports VSS (Volume Shadow Copy Service) in Windows Server 2003, so Windows users can take advantage of the deduplication feature as well.
The same instant replay functionality can be used for servers. Once a boot volume is set up and the operating system is installed for a server, a second bootable volume can be created, and the only additional space used is that which stores the files that are different. For Linux this might amount to a few configuration files, and even for Windows it doesn’t amount to much except for the Windows swap file. This means that you could have several hundred servers booting from one main OS image, and each would maintain only the files that are different. It also means that rolling out patches and updates can be greatly simplified, since only the main image needs to be updated, and the others recloned. Unfortunately, there isn’t yet a way to push changes in the main image out to the clones.
The Compellent Storage Center offers superb ease of use and the widest feature set available in the middle range, without charging a premium price. The wizard-based configuration means that even administrators in small shops who don’t have time to go to storage administration training will be able to set up and use all the sophisticated features available. And the instant replay and automated migration features mean that you can get the best performance where needed and make full use of inexpensive SATA-based storage without any additional effort.
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