Tuesday, April 30, 2013

About SSD hard drive durability

When SSD disks popped up some time ago, many people's main concern was their durability. The claimed 10k write cycles for each block didn't really sound much to most people (including me). Still, I thought I'd risk it, and bought one (an 128GB Crucial/Micron RealSSD m4/C400) about one and a half years ago. The speedup is noticeable, especially for things which need short access times (find, copying large amounds of files, starting applications). Also, it's absolutely silent which is nice too. So from that perspective, I'd say it's definitely worth the money.

But, how about its durability? Of course, I can only really tell about the durability once it breaks, but there is a handy little tool called smartctl which can read various bits of information from the hard drive's self test capabilities. For my device, it reports various things, such as a power-on time of about 5000 hours and a power cycle count of about 2200. The most interesting number, though, is probably the wear levelling count: From what I understand, this is the maximum amount of times a block on the disk has been re-written (you know, of the 10k times it is supposed to survive). Interestingly, after 18 months of daily usage, this is a whopping 53 (sic!) times for the worst-case block. Thus, the controller seems to do an excellent job at wear levelling (if it would be perfect, this 53 would mean an average disk write of 1.3GB per power-on hour, which seems ok; I do quite some IO-heavy tasks and you also have to take the wear levelling overhead into account). Quite impressive, I think!

So: From the block wearout perspective, I don't think there's anything at all to worry about for SSD disks. Mine would survive another 100 years if it's about up to its spec. I guess the controller or something will fail much earlier than the actual memory blocks. And remember: The larger your disk, the better wear levelling is going to work, so this problem will be even less severe.

1 comment:

  1. Interesting, I wonder how this compares to regular spinning drives.

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