By: +David Herron; Date: March 26, 2017
The core issue is that each memory cell in an SSD drive can be written so-many-times. Once each cell is written enough times, that cell dies. The SSD firmware takes care of recognizing dead cells, bypassing those cells when storing data. They also use wear-leveling algorithms to spread write's across the disk and extend its lifetime.
The key to a long SSD lifetime is to leave lots of free space on the drive. This means at least 10% of the disk should be left empty, and perhaps 20% is a good amount to leave free. This is so the wear leveling algorithms can do their thing.
The phrase "over-provisioning" refers to the practice of leaving free space.
These are the key measures which will be contained in the spec sheet:
- DWPD :- How many times you can write an amount of data equal to the SSD drive's capacity over its warranty period
- TBW :- Total data that can be written (total bytes written)
With a DWPD of "2", a capacity of 240 gigabytes, and a warranty of 5 years, you should be able to write 480 gigabytes per day for five years.
lifespan = (capacity x enduranceRating) / averageDailyWrites