Austin S. Hemmelgarn - 17.08.18, 15:01: > 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.
As the data still needs to be transferred to the SSD at least when the SATA connection is maxed out I bet you won´t see any difference in write speed whether the SSD compresses in real time or not. > 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. Who really knows what SSD controller manufacturers are doing? I have not seen any Open Channel SSD stuff for laptops so far. Thanks, -- Martin
