Samsung's 840 EVO SSD is the company's second-generation 3-bit multi-level cell (MLC) SSD, and it's one of the most affordable drives on the market today, retailing for under 50 cents per gigabyte. For example, a 1TB 840 EVO SSD sells for $459 at online retail sites such as Tigerdirect. The EVO line followed the 840 SSD line.
Samsung said in a statement that the read problems occurred on its 2.5-in 540 EVO SSDs and 540 EVO mSATA SSDs because of an error in the flash management software algorithm. "A drop in performance occurs on data stored for a long period of time and [that] has been written only once. SSDs usually calibrate changes in the statuses of cells over time via the flash management software algorithm. Due to the error in the software algorithm, the 840 EVO performed read-retry processes aggressively, resulting in a drop in overall read performance."
Samsung said the problem was confined only to data that had never been rewritten or changed, and there are no problems with reduced read performance if the data was subsequently migrated from those cells or overwritten.
"In other words, as the SSD is used more and more over time, the performance decrease disappears naturally. For those who want to solve the issue quickly, this software restores the read performance by rewriting the old data. The time taken to complete the procedure depends on the amount of data stored," Samsung said.
When it was launched last year, the 840 EVO SSD boasted a new processer that was 33% faster than previous generation non-EVO 840 SSDs. That faster clock speed translated into a 27% increase in the number of input/output operations per second (IOPS), according to Samsung.
Users, however, began complaining about major performance slowdowns, especially with data older than a month. The problem, first reported by tech site AnandTech, introduced average read speeds as low as 158MB/s in a drive rated by Samsung to perform at over 540MB/s.
Complaints about 840 EVO models have filled comment threads on technical forums, such as Overclock.net.
Samsung said its firmware upgrade addresses only the EVO line and not non-EVO 840 SSDs.
Some users on technical blog sites, such as Overclock.net, said Samsung is ignoring the issue on the 840 (non-EVO) SSD. Others were concerned that the firmware fix covers up the bug by simply moving data around the SSD.
That, said one user, means the drive "still is affected with the issue of slowing down when the system is off for weeks or out of the system for a weeks...."
Samsung did not return requests for comment.