Sandforce Life Time Throttling

[sergiu]

And Ao1 did *not* measure compression zero-fill factor, but NAND wear over the course of 64 gb. NAND wear is used as an indication for compression ratio, but it's not necessarily a foolproof one.

@Ao1: Did you do the measurements on a new drive or on one that was already filled before? If the latter then how do we know SMART wear reports are not just from garbage collection doing its work at any time during the last 64 gb (be it because of the 0fill or not)?

Due to its nature, Sandforce compression factor cannot be measured below a threshold limit which is what it can fit to a page. It does not matter if it can compress 32KiB to 10 bytes or 4095bytes because it is using a full page and needs to write it on flash cells. It cannot wait forever to something that is matching the available space to complete it. I am pretty sure it can theoretically compress serveral GB files made by zeroes to a few bytes but it never knows what is receiving next so it must assume the worst possible scenario. And for this reason it will never try to archive more than a fixed value
Regarding the Sandforce GC, it is supposed to erase blocks which would not increase writes count. Also a small but maybe usefull info: I was able run CristalDiskMark (both compressible and uncompressible test data) on a OCZ Vertex 3 240GB model last week. I looked at smart parameters but because I set test size to 100MB I did not expected to see any significant changes, so I did not noted exactly initial values for #233 and #241. But for my surprise, I saw something like 30GB change for incompressible data and 5GB for zero fill. Now values might not be exact because I have not noted them, this is just what I remember from my poor memory. I still have access to the drive but I cannot do any tests, at least now because it is running some VMs.

I have saved the results for later comparison when drive is used: