On 2018-08-17 08:50, Roman Mamedov wrote:
On Fri, 17 Aug 2018 14:28:25 +0200
Martin Steigerwald <mar...@lichtvoll.de> wrote:
First off, keep in mind that the SSD firmware doing compression only
really helps with wear-leveling. Doing it in the filesystem will help
not only with that, but will also give you more space to work with.
While also reducing the ability of the SSD to wear-level. The more data
I fit on the SSD, the less it can wear-level. And the better I compress
that data, the less it can wear-level.
Do not consider SSD "compression" as a factor in any of your calculations or
planning. Modern controllers do not do it anymore, the last ones that did are
SandForce, and that's 2010 era stuff. You can check for yourself by comparing
write speeds of compressible vs incompressible data, it should be the same. At
most, the modern ones know to recognize a stream of binary zeroes and have a
special case for that.
All that testing write speeds forz compressible versus incompressible
data tells you is if the SSD is doing real-time compression of data, not
if they are doing any compression at all.. Also, this test only works
if you turn the write-cache on the device off.
Besides, you can't prove 100% for certain that any manufacturer who does
not sell their controller chips isn't doing this, which means there are
a few manufacturers that may still be doing it.
