Re: HPSS configuration for GCMDC2

[Arie Shoshani <shoshani@lbl.gov>]

Dave,

I have a couple of comments.

dave zimmerman wrote:
> 
> This morning I met with John Riordan to discuss the GC Hpss
> configuration and  the tape situation.
> I learned that it is possible to lock a tape so that no more files will
> be written to it.  This facility can be used to maximize the number of
> tapes available to the GC by transferring say 10 1-Gig files to a single
> tape, locking it and
> moving on to the next tape for the next 10 gig of data.  After the
> GCMDC2 data sinking period is over we would unlock the tapes so that
> they would be available to be filled out.
> 
> If this seems reasonable Id like to follow this plan.

Sounds like a good plan.  But, we should have one tape with enough data
on it, so that we can run a test where we compare reading all the files
from a single tape vs. the files spread out on 5 tapes.


> Regarding the HPSS configuration for MDC2 the proposed configuration is:
> 
> File purging policy:
> Do not purge any file which has been accessed in the last 5 minutes
> Start purge when the cache is 5% full.
> Stop purge when the cache is empty.

If we want to empty the HPSS cache between runs, then "start purge"
should be done when the cache is 0% full, or as close to it as
possible.  As I recall from MDC1 the smallest % possible was 1%.

As for the length of time before purging, the longer the better during
runs, but we need this figure to be low, so that the cache empties
between runs.  I guess we can make this 10 minutes, so that files that
will potentially be shared will stay in cache longer.  This means that
we'll have to wait 10 minutes between runs.  Henrik, Luis: what do you
think?


> Tape drive allocation:
> 5 drives will be available to the StarReco
> a maximum of 3 of those drives will be available for file migration.

Do you mean that we can only write to 3 tapes but read from all 5?
 
> Deferred dismount will be on.  That is, a tape will not be dismounted
> from a drive unless there is a request to mount a new tape in that
> drive.

That's good, so we have no surprises.

Arie.