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Date: Tue, 03 Apr 2012 18:18:43 -0700
From: Julian Elischer <julian@freebsd.org>
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Subject: "trim/discard" success story
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Today I had reason to try the UFS "trim" support on the FreeBSD 
version of the Fusion-IO driver,
and I'm pleased to say that it appears to work just fine..

on a 1.3TB flash card..

the numbers of 'sectors' that the drive considers to hold valid data is
reduced after the contents of the drive is erased..:

After newfs -E:
hw.fusion.fio.fio0.data.stats: [...] 861327 [...]

After writing a few GB to the filesystem but BEFORE"rm -r *"
pu05# sysctl hw.fusion.fio.fio0.data.stats
hw.fusion.fio.fio0.data.stats: [...] 3628354 [...]

After"rm -r *"
pu05# sysctl hw.fusion.fio.fio0.data.stats
hw.fusion.fio.fio0.data.stats:  [...] 919690 [...]

so from 861,327 packets valid to  3,628,354 packets valid, back to 
919,690 packets valid.
(since bitmaps etc are allocated as needed the growth is expected but 
will not grow forever).

(yeah I know it never actually reached 1% full but it was a test, ok?)

for flash drives this is great news..
Now if ZFS would get trim support, that too would be great.