When you are configuring a server, it’s tempting to use SATA instead of SAS drives due to the price difference (and I mean big difference).

Before you choose, let’s look at a few key points: First, NEVER use consumer grade drives for a server unless you enjoy trouble and hardship.

Let’s look at performance: Most enterprise grade SAS drives have more platters, read/write heads and higher spindle speeds than consumer grade SATA drives. They can tolerate more heat, more shock and more wear and tear.  If you pick one up, you will notice that they are MUCH heavier than SATA drives. Finally, consumer grade SATA drives typically spin at 4500-7200 RPM while enterprise class drives spin at 10,000-15,000 RMP. This translates into a huge performance difference.

If performance is not enough to persuade you, consider drive volume and drive life expectancy (here measured in error rate)*:

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* Image and data from Jeffrey Layton article in Enterprise Storage Forum.

The hard error rate is the unrecoverable read errors per bits read. As you can see, consumer drives average 1 error bit per .01 PB’s (1TB) read. If you have a 1TB drive, the odds are likely that you will have an unrecoverable hard error by the time you read/write the equivalent  of the drive’s entire capacity. In a home, where computers are used part time for entertainment, it may take a while to reach that error rate. In a busy server however, the error rate can be reached very quickly.  As you can see by the chart, enterprise class SAS drive has a 100x higher tolerance for hard error rate, this is a huge difference! In a SAS drive, you have to read/write 100x more data before reaching the drive’s error rate.

Consider another scenario: You purchase a server with several SATA drives in a RAID 5 configuration. One of the drives reaches its hard error rate and the controller takes it off line and your RAID array is degraded. You replace it with a new drive and the rebuild process begins. The other drives now all have to transfer huge amounts of data in order to rebuild the RAID array. Since all the drives in the raid were purchased around the same time and have roughly the same amount of data transfer, the additional work may cause one of the other drives to reach or exceed the hard error rate before the rebuild is complete. The other drive fails and you are now looking at two failed drives, a failed RAID array, and a backup restoration scenario.

In conclusion, SATA drives are great because they are cheap and offer abundant storage. But they are not good for server use.

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