Sandforce Life Time Throttling

[sergiu]

I suspect that for compression to be effective the xfer size needs to be 128K or above.

In one of the tests where you wrote zeroes,you were able to use 128GB for 1024GB host writes. For this, I assumed that, if controller is hit in bursts, it will group 8 pages and will archive them, with best case scenario as only one page. But because of granularity of the counter and other internal writes which we did not consider but are counted, this size might be higher and not necessary a multiple of 2. It would be interesting to find out how writes are grouped. For example, let's say that random pages (with archivable content) are written and each 8 pages are compressed to one. Then a secvential read is issued with pages that were archived in different clusters. For this example, controller might need to read one or more pages, decompress them to maybe 32KB or more and retrieve only one peace of 4KB which was part of the secvential read.

Also, some interesting stuff. Below is SMART data from a Corsair Force F240 bought second hand by a friend. Historically, the drive was used in a high end gaming machine for most probably 6 to 9 months. What is most interesting is "Retired block count" value. If it counts 4K pages, then it will go to 0 probably for 32768 taken as value which corresponds to only 128MB, well below spare part. On the other hand, if it is counted as erase blocks of 512KB, then this is almost a full broken die (32Gbit) and this would indicate that controller is able to handle easily up to 4 broken flash dies. As a note, I personally believe drives with Sandforce controllers are best to be bought blindly as second hand. Because of lifetime throttle we can be sure that a 5 years warranty drive which is one year old has at least 80% flash life left.