Why we're switching to SSDs for system disks

November 3, 2013

A commentator on my entry on our future fileserver hardware asked a good question, namely why we're planning to use SSDs for system disks. This is actually likely part of a general shift for us (we've already done it on some new servers). The short version of why is that it is less 'why' and more 'why not'.

SATA hard drives seem to basically have a floor price. 3.5" or 2.5", small or moderately large, you simply can't easily get a decent 7200 rpm drive for less than about $50-$60 (at least in small quantities) no matter how little space you want. The amount of space you get for your $60 has been steadily increasing, but the price has not dropped for small space (instead small HDs seem to have progressively disappeared). As the price per GB of SSDs has shrunk, SSDs that are more than big enough to be OS system disks have now reached this magic $60 price point.

Raw speed and random seek times are usually not an issue for system disks (although we have at least one server where they actually do matter; said server is now using SSDs). However our general assumption is that SSDs are likely to be more reliable than HDs because SSDs don't have that spinning rust hurtling around and around (they also don't get as hot). And being fast doesn't exactly hurt. Since we can get big enough SSDs for the same price as more than big enough HDs, we might as well go with SSDs when it's convenient.

(The relative long-term durability of SSDs versus HDs is at least somewhat uncertain (and they're probably going to fail in different ways). Our HDs have generally lasted as long as we could ask and SSDs have issues like write wear and so on. But on the whole it seems worth taking the chance, especially since there are some benefits.)

Comments on this page:

Word of advice: SSD manufacturer matters even more than with HDDs. One of our vendors configured one our servers with a pair of 64GB SSDs for the OS mirror made by a well known flash storage company. When we first powered up the system, one drive in the mirror was already failed when we first powered it up. Checking the logs, both drives were actually reporting IO errors, so we had to get them both replaced right off the bat. Those replacements ran for about 6 months before both of them failed. At that point I demanded our vendor swap out for a different manufacturer and have been happy ever since (2 1/2 years so far on this pair).

By cks at 2013-11-04 12:14:44:

We've definitely heard this about SSDs and it's one of the drawbacks and annoyances of them today; there are many, with varied quality, and which ones are good keep changing. We've had decent luck so far but it's something we're going to have to keep an eye on.

Written on 03 November 2013.
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Last modified: Sun Nov 3 02:08:03 2013
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