how much of ssd to use?

how much of ssd to use?

[James Harper]

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%?

Thanks

James

Re: how much of ssd to use?

[Brad Campbell]

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.