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Should I defragment my SSD?

Short answer: no, probably not.

The longer answer requires a little more explanation. With hard disks, accessing the next block of data that will pass under the disk head is usually fairly fast, but if the head needs to move at all it can take orders of magnitude longer to read data; a typical consumer disk might be able to transfer upwards of 80MB/s for a contiguous read, but if you need to move the head it could take as long as 10-20 milliseconds. This is the reason that fragmentation causes such a problem on hard disks — it’s dramatically faster to read a file if you don’t have to move the disk head.

On SSDs, the situation is rather different; there is still a performance hit for some types of random access, but the difference is very much smaller. Generally speaking we don’t think it’s likely that the time you’d spend defragmenting your disk would offset the small performance gain you’re likely to see (which might not even be measurable in some cases).

We have heard people talking about how you shouldn’t defragment for fear of “damaging” your SSD. This may have been a problem with some early units, but modern SSDs, according to their manufacturers, will last for decades even if you make them write data flat-out. Most users need not worry too much about flash memory wear — it’s really more of a problem for the manufacturers and their engineering teams.

If you’re interested in how SSDs work, there is an excellent article on Emmanuel Goossaert’s blog.


Posted by alastair at 2015-Mar-23 16:03:09 UTC.