Ease of use
When choosing clustered storage, storage administrators often focus on benefits such as ease of use, scalability or reliability, rather than on the underlying technology.

Jeff Pelot, chief technology officer at the Denver Health Hospital and Medical Center, is phasing out his Fibre Channel (FC) storage in favor of clustered storage from LeftHand Networks. While lower hardware costs were the original goal, lower administrative costs are now the main driver. "I don't know how many [other] people out there are managing 90TB with one person," he says.

HPC users often calculate the performance of clustered storage requirements not by total capacity, but by the GB/sec the system can deliver. The Los Alamos National Laboratory in New Mexico, which simulates the performance of nuclear weapons, needs a specific rate of I/O because it must periodically capture the entire "state" of an HPC compute run (including the contents of RAM) to recover from a failure among the thousands of processors and disks in use, says Gary Grider, deputy division leader of the laboratory's HPC Systems Integration Group.

"It's the [file] system that keeps our calculations stable when processors, memory and the network" fail periodically during the months it takes a complex computing job to run, says Grider.

Parag Mallick discovered that sometimes a vendor's help is required to decide how to distribute data within the file system. Mallick is director of clinical proteomics at the Spielberg Family Center for Applied Proteomics at the Cedars-Sinai Louis Warschaw Prostate Cancer Center in Los Angeles. The organization uses clustered storage devices from Isilon Systems Inc. to store 120TB of data about the proteins found in the blood of cancer patients. Mallick worked with Isilon Systems to design the best directory layout to maximize the predictive caching done by the system, storing the most frequently accessed files in RAM to speed their retrieval.

Different data access needs also call for various clustering technologies. "If I'm supporting a video application, I might want a NAS file server cluster optimized for large throughput of either concurrent streams or one large file being transmitted in parallel," says Schulz.

Clustered storage is a good choice for storage administrators who have "20, 30 or 50 NAS filers ... and really would like to put them up under one namespace," says Grider. He also recommends clustered storage for applications that require many processors/users to write to one file simultaneously, when storage administrators need to scale bandwidth at the same time they scale capacity or if there's lots of meta data to manage.