Brian,
I think you are talking about the case where the dCache is running in
resilient mode. GridPP dCache sites are not (in general) doing this so
cannot set the min and max number of replicas in the system. There is the
potential to run the replica manager on a subset of pools so in theory you
could say that all atlas pools will be controlled such that there are 2
copies of each file while the remainder of the pools only have 1 by
default (the dCache may still create some replicas of some popular files
in order to better load balance the system).
Regarding lcg-infosites, all it does is report the information that each
of the SE are reporting about the used and available storage. The SE GIPS
plugins would have to change to take account of replicas, not
lcg-infosites.
Greig
On Fri, 29 Sep 2006, brian davies wrote:
> Number of replicas can be set in a config file with to values min and max (
> matt doidge can remind me which file but it is also in the dcache book under
> replica manager). this means that the dcache sets a min number and a max
> number of replicas of a file. some sites for redundancy may want to increase
> copies so as to secure file transfer ( raid0 and multiple replicas rather
> than raid5+ and only one copy. Actually, we could get an extra 11.6TB if we
> raid0our storage; but that probably make my storage volatile?) This of
> course would halve the capacity since i would probably need to have a
> replica of each file.
> This is something to point out for those who want to resilient dcache. you
> need to halve/third your disk space to get what you offer to your
> experiment.
> When dcache replicates a file for bandwidth issues, it is a luxury to the
> experiments and so they shouldn't be charged ( ie we don't have to offer
> this service in fact DPM can't do it at the moment iirc). it is a problem
> that we have noticed that lcg-infosites does not take into account
> replicas. First i have heard of experiments being charged for network
> bandwidth.
> brian
>
>
> On 29/09/06, Jensen, J (Jens) <[log in to unmask]> wrote:
> >
> > >> For user requested replication, the fact that there are replicas would
> > >> still not appear in the PNFS namespace of dCache. You really need a DB
> > >> query to pick out _all_ of the files.
> > >
> > > I must agree with Greig as we cant just bill for space used but SHOULD
> > > also bill for bandwidth. Replicas are a consequence of bandwidth.
> >
> > Cost modeling is quite a tricky business - a whole new sub-branch of
> > astrology!
> >
> > So how does the dCache thing work then; do users effectively get
> > Disk2Tape0
> > (at least for certain files, ignore the spaces for now) or are the
> > replicas
> > temporary, for internal optimisations?
> >
> > Can we infer from this that cumulative data in and/or data out should be
> > a metric.
> >
> > -j
> >
>
--
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Dr Greig A Cowan http://www.ph.ed.ac.uk/~gcowan1
School of Physics, University of Edinburgh, James Clerk Maxwell Building
TIER-2 STORAGE SUPPORT PAGES: http://wiki.gridpp.ac.uk/wiki/Grid_Storage
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