Yes.Have dual Samsung 840 Pros on Sonnet Tempo Pro card, installed in 12-core MacPro 5,1, RAID0. Running 10.9.2. Everything is sweet. Single question, enable TRIM on 840s? If yes, which one?
Not quite. The GC doesn't know if a chunk of data that the disk thinks is in use is actually in use by the OS. TRIM let's the OS say that "these chunks are free, go ahead and erase them during GC".Even if you do not use TRIM directly, all modern SSD's have internal garbage collection (IGC) that does the same thing, albeit at a much slower pace.
TRIM has nothing to do with the OS being idle. It means that when the file system in the OS deletes a file, it sends an additional command to the disk saying that the blocks occupied by the file are free, and do not need to be copied during garbage collection.TRIM is nice because it can do it all in one fell swoop because the OS knows when the computer is idle and can call a request for TRIM from the SSD controller. But because the controller doesn't know when the computer is idle it does IGC very sporadically as not to affect user experience.
"Healed" is an interesting term for an operation that contributes to the drive wearing out, but does improve performance in the short term.This is how SSD's were able to function ok over time in RAID 0 before RAID controllers could pass TRIM commands. The 2 drives just healed themselves over time.
Wouldn't the file systems "Table of Contents" (generic term) be enough for the controller to know with a good deal of accuracy what should and shouldn't be there? Because the OS does not get to directly address the NAND in the SSD, the controller dictates where the data actually goes in order to keep wear even across the NAND.Not quite. The GC doesn't know if a chunk of data that the disk thinks is in use is actually in use by the OS. TRIM let's the OS say that "these chunks are free, go ahead and erase them during GC".
Without TRIM, the disk often has to preserve (copy) data that the OS has deleted - since it has no way of knowing that the file system no longer references the blocks on disk.
I think (and this is my opinion) that most people would not care about the hit to NAND endurance the IGC or TRIM causes. It should be trivial to total number of writes each cell can take. Although the fear of NAND endurance decreasing as density increases is justified, for most people, the numbers are still astronomical. I have an early SSD that does not have trim nor a very good, if any, IGC. While it still runs just fine after 5 or so years now, the performance is abysmal. It's down to around 20MB/s write now...sequential."Healed" is an interesting term for an operation that contributes to the drive wearing out, but does improve performance in the short term.