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Storage for plain file servers
Inexpensive file servers that support general office environments--not industrial-strength file servers that support applications such as engineering or multimedia development environments--are perfectly adequate for office application files such as word processing documents, spreadsheets, presentations and HTML files. These types of files are accessed frequently while they are being worked on, but once they are finished, they are rarely accessed again.

Common office application file server storage requirements are less stringent and not all that difficult to meet. Unlike e-mail servers, common file servers don't typically require a large amount of storage capacity, but they do have to support higher performance levels. File servers regularly support a fair amount of I/O work in parallel, particularly when people are beginning their work or preparing to quit. Special business applications that have integrated databases or involve streaming I/O require higher performance levels than average office applications.

NAS appliances work very well as common file servers. The types and degrees of tuning that can be done depend on the product manufacturer and model. The following applies to both NAS appliances and file servers built from commercial software products.

When planning storage for common file servers, you must take into account the strengths and weaknesses

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of the disk drive technologies being used. It's certainly not a mistake to use FC and SCSI drives in file servers because they are much better at handling parallel I/O operations than ATA and SATA desktop disk drives. Subsystem designs can overcome the throughput limitations of ATA and SATA desktop disk drives, but you want to clearly understand what techniques are being used. For instance, ATA and SATA drives could have write caching enabled, which is probably a bad idea because of the chance of data loss. On the other hand, Ciprico Inc.'s new SATA storage subsystem, FibreStore 2212A, is based on an accelerated drive teaming (XDT) technology, and is designed to increase the throughput of SATA-based subsystems for common file serving environments.

One major difference between storage for e-mail and file servers is the amount of cache memory used. While cache doesn't do much for e-mail performance, file servers often benefit from cache. Read-ahead cache is most likely to generate the best results for common office file servers, but if you're trying to improve performance for a particular application, you should ask the application vendor's opinion.

Another way to increase the performance of file servers is to "short-stroke" the drives. The basic idea is to create a single partition on the drive that's approximately one-half to two-thirds of the drive's capacity and ignore the remaining capacity. This reduces seek times in the drive, allowing a large SATA drive to achieve seek times that are similar to SCSI and FC drives.

An important goal for file server storage is to reduce the number of drive failures. As with e-mail server storage, look for SATA drives with MTBF values greater then 1 million hours. Beyond that, file server storage should include hot swapping and hot spare features as standard fare.

iSCSI is also a good fit for file server storage as a way to reduce the cost of putting file servers on a SAN. File server performance over iSCSI should be adequate for most applications, but low latency applications with database functions could suffer with it. Don't bother using TOE unless your servers have processors running at less than 2GHz. iSCSI storage routers that connect iSCSI servers to FC storage are an excellent idea for companies that already have FC SANs. This way you can get the cost reduction of iSCSI on the servers, combined with the high-throughput capabilities of FC and SCSI disk drives.

This was first published in July 2004

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