HomeFiction #3: All SSDs have unbalanced read and write performance
Fact #3: SandForce has balanced read and write peak performance for the life of the drive
The overall performance increase of SSDs over HDDs is fairly well known in the industry. Leading HDDs can deliver about 300 IOPS at peak performance while SSD specifications list 20K-30K IOPS, a 100-fold increase. What is not always clear is that these high IOPS are usually for the read speed of the SSD, but not the writes. In general the write IOPS can be as much as 90% slower than the read speed.
Another less known fact is that most SSDs may start with a very high write performance, but as soon as the drive is used for a few days (or even a few hours), the write speed will be reduced to a small percentage of its original speed.
This drop is caused by a couple of factors. Initially when the SSD is “unwritten” (never been written before, not just all data erased) all the blocks of data are blank and writing to the drive will be at its optimum speed. Unlike a HDD, when writing to flash memory you have to first erase a whole block and then rewrite the new information. In most cases the SSD will write to empty blocks first and then keep track of blocks that contain “old data” for later use. Once each block is written once, the SSD will need to clean up those used blocks. A common term for this process is garbage collection. Once this begins the SSD will drop in performance.
A related factor that reduces the overall performance is the write amplification that occurs with SSDs. If the garbage collection is not efficient, the write amplification can get up to 20 or even higher over the original data written from the host. This high number of writes will create a bottleneck on the flash memory bus and reduce the performance during writes.
DuraWrite combined with other DuraClass capabilities work together to reduce the write amplification of the SSD. The prevents the bottleneck on the flash bus and enables the highest performance during writes even after the advanced SandForce Recycler takes care of the garbage collection.
