Re: BACKUP Throughput measurement

From: John Brandon (brandon_at_dalsemi.com)
Date: 09/29/03 

Date: Mon, 29 Sep 2003 11:33:38 -0500

Chris Sharman wrote:
> Doesn't take account of /nobackup files (dump,page,swap & any
> site-specific).

That is correct - and in a one or two disk environment you would have some
erroneous data however we have at least 40 drives and that helps to balance out
the no-data-backup.

> A count of io to the tape device, together with knowledge of the
> blocksize specified to backup, and the /verify setting, gives an
> apparently accurate figure for the (uncompressed) data written to tape.

Now I find this an attractive idea - however would not the I/O be misleading?
Would not the I/O include non-tape I/O? I would believe that there is I/O from
disk? How would one account for that? I would assume division by two but I
know beter - not always that easy and I/O from disk is certainly different than
I/O to tape.

What about the group size - that would also have a play on things.

Then the block size - from scanning the openvms.org archives I find that a
block size above 32K (aprox) has little or no impact...

J*o*h*n B*r*a*n*d*o*n
VMS Systems Administrator
firstname.lastname.spam.me.not@dalsemi.com

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