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From: idall@augean.OZ (Ian Dall)
Newsgroups: comp.sys.nsc.32k
Subject: Tapes on ICM-3216
Message-ID: <168@augean.OZ>
Date: Mon, 4-May-87 23:03:01 EDT
Article-I.D.: augean.168
Posted: Mon May  4 23:03:01 1987
Date-Received: Sat, 9-May-87 02:48:55 EDT
Reply-To: idall@augean.OZ (Ian Dall)
Distribution: world
Organization: Engineering Faculty, University of Adelaide, Australia
Lines: 48
Keywords: backups, scsi, ICM-3216, V.2


Backing up to tape on an ICM 3216 under Unix V.2 using volcopy takes a lot
longer than it should.

If I use the ROM monitor:

	C 1:0:1 7

It takes about 5 minutes to copy 19 MBytes. Which establishes the
speed of the hardware.

If I use the volcopy program:

	19 MBytes takes 17 minutes.

The tape keeps stopping, backing up and starting again.

I presume I am not specifying suitable options for volcopy. I don't understand
many of the options most of which don't seem applicable to QIC-24 cartridges.
I used a blocking factor of 10 (should this be increased?), and in response
to the queries specified 2400ft and 8000bpi (which I assume it makes no
constructive use of (with these drives) except to see whether your filesystem
will fit into one tape or not).

Any one else use volcopy? What options do you use and what performance do you
get. Perhaps volcopy is not very intelligent and doesn't know that SCSI devices
can copy between themselves without going through CPU memory -- in which case
perhaps this is a limitation of Unix (it does seem a bit difficult to see how
direct device to device copies could fit into Unix's idea of treating devices
as (special) files). As it stands it would be quicker (though less convenient)
to halt, use the ROM monitor and reboot. 

Another question: When one creates a file system, mkfs defaults to 400blks/cyl
and 8 blk gap. Do these numbers have any significance for an intelligent
drive (such as scsi) especially when the disk drive has significant (16kB)
buffers? Is the rotational gap the same as interleaving (which can be handled
by the disk drive) and should the blocks/cylinder be the number of usable blocks
(ie excluding bad block replacement) or the number of physical blocks?
I used the defaults and it doesn't seem to worry it but could I get better
performance by altering them?

Perhaps some of these questions belong in unix.wizards which I will try if
no one reading this news group can help.

Thanks,
	Ian Dall

	idall@augean.OZ .