On Sep 7, 2009, at 10:20 AM, Bob Friesenhahn wrote:
On Mon, 7 Sep 2009, Richard Elling wrote:
This is an article about the new TRIM command. It would be
important for
file systems which write their metadata to the same physical
location or use
a MRU replacement algorithm. But ZFS is copy-on-write, so the
metadata is
allocated from free space and ZFS is transactional, not directly
MRU. It is
The purpose of the TRIM command is to allow the FLASH device to
reclaim and erase storage at its leisure so that the writer does not
need to wait for erasure once the device becomes full. Otherwise
the FLASH device does not know when an area stops being used.
Yep, it is there to try and solve the problem of rewrites in a small
area,
smaller than the bulk erase size. While it would be trivial to
traverse the
spacemap and TRIM the free blocks, it might not improve performance
for COW file systems. My crystal ball says smarter flash controllers
or a
form of managed flash will win and obviate the need for TRIM entirely.
-- richard
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