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How do you evaluate a hard drive's performance? I'm thinking of buying an SSD, but I want to know what the very basic statistics that I should pay attention to are. I've heard of many of them such as Random Seek, Sequential Seek and their write equivalents, but which actually matter for a user desktop?

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up vote 4 down vote accepted

The whole point to an SSD is that the latency is near 0 typically very low, especially when compared to conventional HDD's. There is no "seek time" because there is no disk spinning under a fixed read head. This is why they are so fast compared to conventional hard drives. Refer to this FAQ, it includes some good basic information about SSD'd as well as links to resources you can use to evaluate their performance. It also has a nice writeup about the differences between conventioanl drives, SSD1 & SSD2.

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0 latency is not entirely true. Because most controllers on SSDs operate in blocks of a certain size (sometimes larger than you might think) there is some latency for small reads as the device will internally read a whole block even just to pull a few bytes out. This is usually countered by the read block being held in some amount of cache so is available without re-read if needed again soon, but for some IO patterns the difference can be quite noticeable. This effect is usually even worse for writes. But this factor is still very small compared to physical latency on spinning disks. – David Spillett Nov 19 '09 at 0:32
Concur. That's why I said 'near 0'. But even 'near 0' is not true once you fill up your SSD & you have to clear blocks of data before you can write new ones. That's why many types of SSD's now have garbage collection features built in. A long winded way of saying your are right - I'll strike that. – DaveParillo Nov 19 '09 at 0:46

As AnandTech and other review sites point out, the random read/write speeds are key to general performance - and this is where SSDs are spectacular compared to HDDs. (This is a result of the tiny latency that DaveParillo describes.) The sequential read/write values tend to be good for SSDs, but are only a concern under relatively rare scenarios (such as copying a large file or hibernating the OS).

For general desktop performance, this AnandTech page illustrates the huge benefits that an SSD will provide.

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