Don’t Fill Them to Capacity
You should leave some free space on your solid-state drive or its write performance will slow down dramatically. This may be surprising, but it’s actually fairly simple to understand.
When an SSD has a lot of free space, it has a lot of empty blocks. When you go to write a file, it writes that file’s data into the empty blocks.
When an SSD has little free space, it has a lot of partially filled blocks. When you go to write a file, it will have to read the partially filled block into its cache, modify the partially-filled block with the new data, and then write it back to the hard drive. This will need to happen with every block the file must be written to.
In other words, writing to an empty block is fairly quick, but writing to a partially-filled block involves reading the partially-filled block, modifying its value, and then writing it back. Repeat this many, many times for each file you write to the drive as the file will likely consume many blocks.
As a result of its benchmarks, Anandtech recommends that you “plan on using only about 75% of its capacity if you want a good balance between performance consistency and capacity.” In other words, set aside 25% of your drive and don’t write to it. Only use up to 75% of your drive’s free space and you should maintain ideal performance. You’ll see write performance start to slow down as you go above that mark.
