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.
So it seems to me that having this feature per-file is really useful.
Say i have a presentation to give in Pleasanton, and the presentation
lives on my single-disk laptop - I want all the meta-data and the actual
presentation to be replicated. We already use ditto blocks for the
meta-data. Now we could have an extra copy of the actual data. When i
get back from the presentation i can turn off the extra copies.
Doing it for the filesystem is just one step higher (and makes it
administratively easier as i don't have to type the same command for
each file thats important).
Mirroring is just like another step above that - though its possibly
replicating stuff you just don't care about.
Now placing extra copies of the data doesn't guarantee that data will
survive multiple diskf failures; but neither does having a mirrored pool
guarantee the data will be there either (2 disk failures). Both methods
are about increasing your chances of having your valuable data around.
I for one would have loved to have multiple copy filesystems + ZFS on my
powerbook when i was travelling in Australia for a month - think of all
the digital pictures you take and how pissed you would be if the one
with the wild wombat didn't survive.
Its maybe not an enterprise solution, but it seems like a consumer solution.
Ensuring that the space accounting tools make sense is definitely a
valid point though.
eric
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.
--matt
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
