On Mon, 25 Jul 2011, Edward Ned Harvey wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Erik Trimble
Honestly, I think TRIM isn't really useful for anyone.
I'm going to have to disagree.
As usual. :-)
There are only two times when TRIM isn't useful:
Hopefully you would agree that if there is a request to overwrite 128K
of existing data that the SSD can then know that the FLASH pages which
would be overwritten are no longer needed? This is step three of the
three step process.
In case #2, it is at least theoretically possible for devices to become
smart enough to process the TRIM block erasures in parallel even while there
are other operations taking place simultaneously. I don't know if device
mfgrs implement things that way today. There is at least a common
perception (misperception?) that devices cannot process TRIM requests while
they are 100% busy processing other tasks.
TRIM is really hard to do safely and efficiently. Consider that a
drive may still have many pending TRIM requests while subsequent
requests come in to write to those same areas. Improper re-ordering
of TRIM and write requests can destroy data. This makes
high-performance TRIM difficult to do in a low-cost product.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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