One thing to remember in this discussion about SSD longevity is that the
underlying value of interest is the total number of erase cycles, per
block, on the flash devices. Vendors quote lifetime as a number of
bytes, but this is calculated using an assumed write amplification
factor. That constant varies with the workload, and I suspect that a
database WAL will not produce the value used in the vendor marketing
material. I don't think you can simply say that I am writing so many Gb
WAL files, therefore according to the vendor's spec the device should
have lifetime of X years -- presumably you'd need to know how many
fsync() calls per second were being made, and then how those translate
to flash block erase rate on the far side of the SSD controller firmware.