SSD Lifetime Estimation Revisited

Back in 2013 I wrote a post about how long I thought my SSD would last based on the amount of data I write to the drive on a daily basis. Back then my daily write rate was 10 GB a day and based on a calculation method of Anandtec I estimated the lifetime of my SSD to be at least 14 years. In the meantime others have done practical tests of how many write cycles SSDs really endure before they die so I came back to the topic once more with my usage scenario.

Things are a bit strange on my system as depending on where I look I get different numbers. On the file system level there’s the following command to get the number of bytes written to a partition:

sudo tune2fs -l /dev/xxx  [replace xxx with the partitions of a drive]

The second one looks like this and should give the same result:

cat /sys/fs/ext4/sdaXXX/lifetime_write_kbytes [replace xxx with the partitions of a drive]

In my case the accumulated file system level values show that 36 TB of data were written to the two main partitions I use on my SSD over 2 years. That would be 46 GB a day. That’s a lot more than the 10 GB I measured a couple of years ago but it does not seem to be out of the ordinary according to this article on Heise (in German).

At first I had no idea what could possibly write 46 GB a day to my SSD so I had a closer look at the block level write counter for a couple of days with the following command:

# data written to sda since the last reboot in GB
awk '/sda/ {print $3"\t"$10 / 2 / 1024 / 1024}' /proc/diskstats

Here, I still get the 10 GB a day on average. Once a week however, a TRIM is made, which makes this counter jump tremendously. Mystery solved. Probably, TRIMs do not count towards the data written to the SSD but since I’m not entirely sure, let’s assume the worst case and include it. Fortunately it turns out that even if my usage is 5 times higher than measured on the block level without TRIMs, I’m still on the safe side. Samsung says that my 1 TB 850 Evo drive has a write endurance of 150 TB. And the Heise article already linked to above says that even this is a gross understatement, as the predecessor of my SSD was guaranteed by Samsung to endure 70 TB of data written to it and in reality only failed after writing over 1200 TB of data to it.

So if I take Samsung’s number I’m good with my 850 Evo for at least 8 years, and far more than 60 years if I take the Heise numbers. Both values are reassuring as I hope that at least in another 5 years, SSDs will have become cheaper again so I can upgrade from my 1 TB to at least a 2 TB drive. I’d do it today but the price for a 2 TB SSD is still around €600 where it has been for several years now. Not that I would have much of a choice in 5 years anyway as by then I expect that most notebooks will no longer support 2.5″ drives and instead have fully migrated to the m.2 format.