The Samsung SSD 840 is the first widely available SSD series that uses TLC memory chips, where each memory cell can store three bits. TCL flash memory doesn't last as long as the traditionally-used MLC flash memory, but it's cheaper which translates to lower SSD prices. Samsung claims that the 840 SSDs are super-reliable despite the use of TLC memory, but consumers aren't quite convinced yet. There really is only one way to find out exactly how many times you can write to an SSD 840 before it calls it a day.
Hardware.Info took two Samsung SSD 840 250GBs and started writing to them last night. It's a continuous writing test, so we won't stop until they break. Yes, it can take several months, but we won't stop until we find out. We put up a live video stream so that anybody that's interested can follow our progress.
In our review of the Samsung 840 SSD 250GB we calculated the potential lifespan of the SSD. Samsung informed us that they did not agree with our calculations. The TLC chips in the 840 SSDs are validated for a minimum of 1,000 write cycles, and the wear-leveling algorithms work in such a way that even when the SSD is almost full it won't have a significant negative impact on the lifespan. Wear leveling moves 'permanent' data after a period of time so that all cells are used equally often for new write tasks. Samsung was not able to provide an improved version of our calculations, so they left us with no choice but to push a couple Samsung SSD 840s to their bitter end to find out how long that takes in real life...
In our laboratory we set up two systems, with one Samsung SSD 840 250GB each. We put 121 GiB of permanent data on each SSD, to simulate a scenario in which the SSD is about half full. With Anvil's Storage Utilities, we continuously write to both SSDs. We leave at least 12 GiB of free space.
Write 'til you drop
We configured the Hard Disk Sentinel software to continually read the health of the SSD from the S.M.A.R.T. data. Samsung says that this health score is linked to the number of write cycles that each flash cell has had. When each cell has been through 250 out of the 1,000 validated cycles, the health is 75. At 500 cycles for each cell the health score is 50, and so on. When health reaches 0, it means that the 1,000 validated cycles have been reached. That does not automatically mean that the SSD is broken now.
To determine whether an SSD has reach the end of its life, we do the following. After every 50 loops of 30 seconds of writing, Anvil's Storage Utilities determines the MD5 hash of a permanent 1 GB file, and compares it to the previously determined and correct hash. When that hash no longer corresponds, it means that data corruption has occurred and that the SSD is done for.
With the Sentinel software we use the S.M.A.R.T. data to keep track of how many terabytes of data have been written to the SSDs in total. Anvil also tracks how much data has been written by the test. The S.M.A.R.T. data will be higher, and that's because moving existing data for wear-leveling also counts as writing. In the Anvil software we therefore primarily look at the amount of written data.
Left the Hard Disk Sentinel software which checks the health of the SSD, and on the right Anvil's software which continuously writes to the 840 SSDs.
It's generally accepted that the average consumer writes an average of 5 to 10 GB per day to an SSD. You have to try quite hard to exceed 10 GB per day. If we take that 10 GB per day, and 365 x 10 = 3,650 GB = 3.56 TB. That's one year of average writing, which we can simulate with the test software. This should allow us to establish what the actual lifespan is of these SSDs.
We will report on our findings every two weeks. You can also keep track of the progress in the meantime, as we put up a live stream of one of the two test systems. See below! And please let us know your thoughts in the comment section.
Update June 11: The primaty SSD of which we streamed the test, has failed. The livestream has therefor ended and will not return. Please see the latest update for more information.