Matthew Ahrens 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.
This is unfortunate. As a laptop user with only a single drive, I was
looking forward to it since I've been bitten in the past by data loss
caused by a bad area on the disk. I don't care about the space
consumption because I generally don't come anywhere close to filling up
the available space. It may not be the primary market for ZFS, but it
could be a very useful side benefit.
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 don't see much need for this in any area that I would use ZFS (either
my own personal use or for any case in which I would recommend it for
production use).
However, if you think that it's OK to under-report free space, then why
not just do that for the "data ditto" blocks. If one or more of my
filesystems are configured to keep two copies of the data, then simply
report only half of the available space. If duplication isn't enabled
for the entire pool but only for certain filesystems, then perhaps you
could even take advantage of quotas for those filesystems to make a more
accurate calculation.
--matt
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