On 02/03/13 14:19, James Harper wrote:
I've read that SSD drives work best when you only use some percentage of them (75%, 50%, etc) because by leaving unused space it allows the SSD more headroom to shuffle data around internally to keep things optimal. Those articles are most likely written for a filesystem on an OS that might not know about TRIM/UNMAP etc. Has anyone done any testing on sustained random write throughput on a (say) 60GB flash drive with only 50% dedicated to bcache, or 75%, or 100%?
SSD's use spare space to shuffle things around so they can reclaim space freed in sizes less than a full erase block. Bcache explicitly uses big buckets in such a way as to remove the requirement for this. Nothing is freed in a way that would cause fragmentation of the sector space, so no re-organising is required on the part of the drive.
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