I use my SSD to read and write at the same time, and I found that writing influences read performance quite a lot.
Example:
Without write, my read may be X MB/s, but with write, my read became 0.5X MB/s. And the Read performance would be influenced more if the write speed is higher (I control the write speed in my program).
Dose any one know why this happens?
Your SSD is almost certainly connected via SATA. SATA uses the same wires for reading as for wrting, which means the reads and writes have to be interleaved in time.
SSD drive performance is mostly determined by two factors: the speed of the memory in the drive and the performance of the memory controller and firmware built into the drive. The memory speed is essentially static, but the firmware code can be improved. Additionally, drives perform worse at or near full capacity, and sometimes continue to perform badly after space is freed up.
Manufacturers often update the firmware on a drive to address issues such as yours. An example of Intel releasing a patch to fix mixed read/write performance is described here: http://www.tomshardware.com/reviews/ssd-performance-power,2279-2.html Manufacturers usually offer firmware updates utilities that are easy to use, but be sure to read the details about the firmware as they are sometimes a destructive upgrade: all of the data on the dive may be erased.
There are usually test results for SSD drives on popular hardware sites. Assuming your drive is relatively mainstream you can read those results to determine if the performance of your drive is normal. You can also compare the SATA controller hardware in your computer with that used in the tests, though that is less likely to be a problem unless you are using an older computer or enterprise level server hardware.
Finally you should also consider using a different SATA cable, different cable routing within the comouter, or even temporarily move the drive into another machine for testing purposes (the two former options do not apply to laptops).
