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Balancing SATA and SCSI

Selecting the right combination of SATA and SCSI disk drives in your system is critical. This tip offers suggestions on how you can strike an effective balance.

What you will learn from this tip: Selecting the right combination of SATA and SCSI disk drives in your system is critical. This tip offers suggestions on how you can strike an effective balance.

Do you want to use SCSI or SATA hard disk drives on your system? Increasingly, the answer is that you want both. The SCSI and SATA interfaces, and the drives built to use them, are different enough that their characteristics can complement each other, providing acceptable performance at a significantly lower total cost.

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Of course, that assumes you've chosen the correct mix of SCSI and SATA drives. If you get it wrong, you pay too much for storage or you can't meet your users' needs cost effectively.

For applications demanding high performance, such as critical parts of a DBMS or real-time video editing, SCSI is still the drive of choice. Not only is the interface faster, but SCSI drives tend to be optimized for throughput, while SATA drives are generally optimized for cost.

For jobs needing lots of storage at reasonable cost, such as disk-to-disk backup, SATA has the advantage. However, in a lot of cases you can't simply choose which type of disk based on the application. Different parts of applications can benefit from different kinds of drives.

For example, in Microsoft Exchange, the transaction files are central to performance and need all the speed they can get. However, the message databases are much less critical to overall performance and often they can be run on SATA drives. Since messages use a lot more storage than the transaction log, this can result in substantial savings. Rather than looking at your storage needs by application, it makes more sense to drill down to the mix of needs within each application.

The size of the drives is also a consideration. SATA drives tend to follow the ATA philosophy of "pack everything onto one big drive," with sizes of up to 750 GB. This is fine for desktops and a lot of applications, but for applications needing the fastest access, such as database log files, you want to trade spindles for capacity because it improves performance. The problem is that it's getting harder to get ATA drives in smaller capacities, say 75 GB or less.

With SCSI, on the other hand, you have a lot of choices in the 60-75 GB range; you're a lot more limited if you want anything larger than 300 GB. You may find yourself using SCSI drives simply because they're easier to get in the capacities you want.

The logical question is how much money can you save by doing all this? Unfortunately, that's hard to calculate because the ideal mix of SATA and SCSI is going to vary from enterprise to enterprise. As a first approximation, you can say that SATA drives are cheaper than the more-or-less equivalent SCSI by roughly 50%. ("More or less" because SCSI and SATA drives, even from the same manufacturer, really aren't equivalent, except in capacity.) Besides the disks themselves, other SATA-specific system components, such as arrays, are also generally less expensive than their SCSI counterparts.

Serial ATA (SATA) is a drive interface designed to replace the Parallel ATA physical storage interface. The storage world has been buzzing about SATA drives for years, debating how it stacks up against other technologies.

Users of the SATA interface are benefiting from greater speed, simpler upgradeable storage devices and easier configuration. While SATA drives don't match the performance of Fibre Channel (FC) hard drives, they provide the low cost per gigabyte and high storage densities crucial for "near-line" storage tasks such as performing backups and archiving.

This Fast Guide is a compilation of SATA-related tips that have appeared on As our site devotes more coverage to SATA, expect to see more tips related to upgrades and configuration.

Fast Guide: Managing SATA drives

  Balancing SATA and SCSI
  Fixing conflicts between older and newer SATA drives
  SATA technology advances and expands in the enterprise
  Plugging into external SATA
  Choose SCSI over SATA for enterprise servers
  SATA can fill storage upgrade for older computers
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About the author: Rick Cook specializes in writing about issues related to storage and storage management.

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