Allocating uninitialized file blocks
Posted Apr 20, 2012 21:45 UTC (Fri) by Cyberax (✭ supporter ✭, #52523)
However, TRIM command can't be queued. So it probably makes no sense to use it for large allocations and/or to keep a pool of recently-trimmed pages for immediate small allocations.
Posted Apr 20, 2012 21:51 UTC (Fri) by dlang (subscriber, #313)
The SSD does keep a pool of unused pages for new allocations. What trim does is it lets the SSD know that you no longer care about the data on that block, and so it can add the block back to that pool.
If the SSD runs out of this pool, writing slows drastically as it must first erase a block before it can write anything. If you are expecting to do a LOT of writing to a SSD, you may want to make sure that you partition it to something less than the advertised size so that that extra space will remain in the pool (this works as long as that extra space has never been written to, or is explicitly relased via a TRIM command)
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