On Dec 30, 2009, at 10:53 AM, Andras Spitzer wrote:
Devzero,
Unfortunately that was my assumption as well. I don't have source
level knowledge of ZFS, though based on what I know it wouldn't be
an easy way to do it. I'm not even sure it's only a technical
question, but a design question, which would make it even less
feasible.
It is not hard, because ZFS knows the current free list, so walking
that list
and telling the storage about the freed blocks isn't very hard.
What is hard is figuring out if this would actually improve life. The
reason
I say this is because people like to use snapshots and clones on ZFS.
If you keep snapshots, then you aren't freeing blocks, so the free list
doesn't grow. This is a very different use case than UFS, as an example.
There are a few minor bumps in the road. The ATA PASSTHROUGH
command, which allows TRIM to pass through the SATA drivers, was
just integrated into b130. This will be more important to small servers
than SANs, but the point is that all parts of the software stack need to
support the effort. As such, it is not clear to me who, if anyone,
inside
Sun is champion for the effort -- it crosses multiple organizational
boundaries.
Apart from the technical possibilities, this feature looks really
inevitable to me in the long run especially for enterprise customers
with high-end SAN as cost is always a major factor in a storage
design and it's a huge difference if you have to pay based on the
space used vs space allocated (for example).
If the high cost of SAN storage is the problem, then I think there are
better ways to solve that :-)
-- richard
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