On 9/12/06, Matthew Ahrens <[EMAIL PROTECTED]> wrote:
Matthew Ahrens wrote:
> Here is a proposal for a new 'copies' property which would allow
> different levels of replication for different filesystems.
Thanks everyone for your input.
The problem that this feature attempts to address is when you have some
data that is more important (and thus needs a higher level of
redundancy) than other data. Of course in some situations you can use
multiple pools, but that is antithetical to ZFS's pooled storage model.
(You have to divide up your storage, you'll end up with stranded
storage and bandwidth, etc.)
Given the overwhelming criticism of this feature, I'm going to shelve it
for now.
I think it's a valid problem. My understanding was that this didn't
give a *guaranteed* solution, though. I think most people, when
committing to the point of replication (spending actual money), need a
guarantee at some level (not of course of total safety; but that the
data actually does exist on separate disks, and will survive the
destruction of one disk). A good solution to this problem would be
valuable. (And I'd accept a non-guarantee on a single disk; or rather
a guarantee that said "if enough blocks to find the data exist, and a
copy of each data block exists, we can retrieve the data"; but that
guarantee *does* exist I think).
Out of curiosity, what would you guys think about addressing this same
problem by having the option to store some filesystems unreplicated on
an mirrored (or raid-z) pool? This would have the same issues of
unexpected space usage, but since it would be *less* than expected, that
might be more acceptable. There are no plans to implement anything like
this right now, but I just wanted to get a read on it.
I was never concerned at the free space issues (though I was concerned
by some of the proposed solutions to what I saw as a non-issue). I'd
be happy if the free space described how many bytes of default files
you could add to the pool, and the user would have to understand that
results would differ if they used non-default parameters. You're
probably right that fewer people would mind having *more* space than
an unthinking reading would show than less.
--
David Dyer-Bennet, <mailto:[EMAIL PROTECTED]>, <http://www.dd-b.net/dd-b/>
RKBA: <http://www.dd-b.net/carry/>
Pics: <http://www.dd-b.net/dd-b/SnapshotAlbum/>
Dragaera/Steven Brust: <http://dragaera.info/>
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