(Displaimer: Maybe I missed the point or misunderstood something)
Do simple test, you need only your imagination:
You have 100GB big dataset on your (mainframe) DASD. You keep there some
AVI movies. The SYS1.MOVIE dataset occupy ~100GB on DASD, ~100GB will be
transmitted through the FICONs channels, ~100GB on VTS disk cache and
finally ~100GB on backend tape.
Now you have SYS1.NORMAL dataset with typical, compressible data, let's
assume 4:1 compression
So, ~100GB on DASD
~100GB sent by channel cards from the CPC
~100GB received by channel adapters by the VTS
(compression in-flight)
~25GB stored on VTS disk cache
~ 25GB of data can be destaged on backend (real) tape.
Now what about RMM?
RMM should show you dataset size ~100GB in both cases. That's the size
of your dataset, not the space occupied by the dataset on any medium.
Just number of blocks * blocksize (assuming equal blocks).
What about VOL size, free space on the volume? That's ...irrelevant!
Your volumes are virtual, you don't care about free space left on the
tape volume, because the space does not exist and does not waste any
resource.
What about backend tape? Well, that should be VTS responsibility. ;-)
--
Radoslaw Skorupka
Lodz, Poland
W dniu 2013-07-18 01:01, Munish Sharma pisze:
Hello
I am researching on TS7740 VTS, as it reaching the VTS Throughput limit and
done some initial analysis with VEHSTATS.
To narrow down to alias level reporting, for who is using how much at what
point of time..I am using RMM report. I am struck at a point, where I do not
understand.. if RMM says in panels a DSN is 100GB, but in RMM report DSIZE is
zero (most cases) .. and comparatively minimum data(lets say 6-7 GB), under
Variable(Actual amount of Data on Tape) .. in RMM report.
So, If RMM Panels says TAPE DSN was 100 GB.. but 6-7 GB on real tape.. I
understand compression does that..
NOW the question is ... DOES VTS do any I/O initially while creating 100GB or
is it compressing while write to VTS and not creating 100GB( just fake it )..
So does that do I/O for 100 GB while writing to VTS or 25gb as if compressed?
Another scenario.. If a Compressed Data on Backend tape was 3982 MB and 25244
MB in VTS.. after coming to VTS .. Does this DSN uses 25 GB space in VTS or
virtualization keep it at 3982 MB even in VTS (just fake it)... So, when Host
going to read it back, does it read 25GB, or 3982 MB?
Please let me know, how to look at it..
Regards
Munish Sharma
People are Awesome....
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