I’ve talked about our high speed solid state drive array previously. In general it’s been working well since we set it up. However, a few weeks ago, after a fair amount of use, we discovered that its speed had dropped to 400 MB/sec from 2100 MB/sec when we set it up. Since we want to be able to collect data at 1100 MB/sec, this was a problem. I’m pretty sure that the problem is related to the way SSDs store data. Unlike magnetic hard drives, SSDs can’t just overwrite previously written areas – they must be erased first. This means that if you fill up an SSD, delete some files, and then want to write more files to the disk, the previously used areas must be erased first. However, erasing is slower than writing, so this erasing slows down performance of the drive. For a good intro to SSDs and how they work, see this article.
Consistent with this, erasing our SSD RAID0 array through the RAID controller control panel and reformatting the disk (so that Windows could recognize it) restored it to its original performance. However, it would be nice if there was a way to deal with this that didn’t require spending an hour erasing the drive. Continue reading