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Comment by arete | Hacker News Reader

AnandTech and other sites have mentioned that newer drives (Sandforce in particular) do background garbage collection which eliminates some of the need for TRIM - but does require idle time.

I'd say go for the SSD. I just upgraded to a 240GB OCZ Vertex 2 and the speed boost is almost unbelievable.

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Background garbage collection doesn't help so much if your drive doesn't know which logical blocks no longer contain active data - which is what TRIM is all about.

(Filesystems historically never worried about informing floppy disks or hard disks about deleted sectors / blocks, because there was nothing useful those storage mediums could do with the information).

ssd's have spare blocks for extra life/wear leveling. ssd garbage collection can use LBA in combination with these spare blocks to always have cleared blocks.

Sure, but it still has to waste time (and cell life) consolidating and moving about logical blocks that the filesystem no longer cares about.

GC only works while the drive is idle and should improve cell life drastically because you do a whole lot less read/modify/write cycles for small writes in the long run. Assuming a 256 GB drive with a write endurance of 1,000,000 cycles and a write speed of 200 MB/s, it would take on average 40 years to burn out the drive by sequentially overwriting its contents. The problem with read/modify/write is that if you are doing random writes of 4 KB with an erase block size of 512 KB at 50 MB/s, the effective internal write speed is 6 GB/s and you will burn out your drive in 1-2 years instead of 40. A full GC cycle is essentially a sequential rewrite of the drive. Let's say a full cycle frees up 16 GB, as 4 GB overprovisioning per 64 GB is standard. You can write 16 GB without any read/modify/writes, and for every 16 GB you write, you will have to do an additional 256 GB of writes for the GC cycle. That sounds awful, but compared to a bunch of read/modify/writes the drive life will go up by a factor of 8. The average write speed will also be higher. To avoid long pauses the GC only runs when the drive is idle, so for things like database servers trim is essential, but on a laptop/desktop GC is plenty good enough.

I may have been unclear - I'm not denying that GC is a good thing, but GC with TRIM is substantially better again than GC without. TRIM is just a way of putting more blocks into the G, to be C'd.

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