On Tue, 12 Sep 2006, Matthew Ahrens wrote:
> Torrey McMahon wrote:
> > Matthew Ahrens wrote:
> >> 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.)
> >
> > Can you expand? I can think of some examples where using multiple pools
> > - even on the same host - is quite useful given the current feature set
> > of the product. Or are you only discussing the specific case where a
> > host would want more reliability for a certain set of data then an
> > other? If that's the case I'm still confused as to what failure cases
> > would still allow you to retrieve your data if there are more then one
> > copy in the fs or pool.....but I'll gladly take some enlightenment. :)
>
> (My apologies for the length of this response, I'll try to address most
> of the issues brought up recently...)
>
> When I wrote this proposal, I was only seriously thinking about the case
> where you want different amounts of redundancy for different data.
> Perhaps because I failed to make this clear, discussion has concentrated
> on laptop reliability issues. It is true that there would be some
> benefit to using multiple copies on a single-disk (eg. laptop) pool, but
> of course it would not protect against the most common failure mode
> (whole disk failure).
... lots of Good Stuff elided ....
Soon Samsung will release a 100% flash memory based drive (32Gb) in a
laptop form factor. But flash memory chips have a limited number of write
cycles available, and when exceeded, this usually results in data
corruption. Some people have already encountered this issue with USB
thumb drives. Its especially annoying if you were using the thumb drive
as a, what you thought was, a 100% _reliable_ backup mechanism.
This is a perfect application for ZFS copies=2. Also, consider that there
is no time penalty for positioning the "heads" on a flash drive. So now
you would have 2 options in a laptop type application with a single flash
based drive:
a) create a mirrored pool using 2 slices - expensive in terms of storage
utilization
b) create a pool with no redundancy
create a filesystem called "importantPresentationData" within that pool
with copies=2 (or more).
Matthew - "build it and they will come"!
Regards,
Al Hopper Logical Approach Inc, Plano, TX. [EMAIL PROTECTED]
Voice: 972.379.2133 Fax: 972.379.2134 Timezone: US CDT
OpenSolaris.Org Community Advisory Board (CAB) Member - Apr 2005
OpenSolaris Governing Board (OGB) Member - Feb 2006
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