ISA 1542C for SCSI tape

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From - Mon Aug 27 11:11:46 2001
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Newsgroups: comp.unix.sco.misc
From: bill@wjv.com (Bill Vermillion)
Subject: Re: Can I use an Adaptec 1542CP in an SCO OpenServer 5.0.6 box?
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Date: Mon, 27 Aug 2001 12:37:37 GMT
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In article <3B89D98C.DCF73C8A@home.com>, Michael Sweeden
<michaelsweeden@home.com> wrote:

>I have a system that used to backup, then began to fail on occasion
>when backing up, and now has progressed to the point of locking up
>the entire system on occasion and usually failing. This lockup has
>occurred both with Unix tar and with BackupEdge software. System
>is an OpenServer 5.0.6 Enterprise box with an Exabyte 8mm DAT tape
>unit with hardware compression attached to an onboard "alad160"
>host adapter. The hard disk system is a RAID 0 on an Adaptec
>3200S controller. The tape drive and media have been changed to
>no avail. I wish to see if the onboard SCSI adapter has a problem
>by disabling it and installing an ISA Adaptec 1542CP adapter I
>have - can anybody tell me if 5.0.6 supports it, and if so, how to
>configure 5.0.6 for it? Any ideas on this problem would also be
>appreciated. The system is rock solid except when backing up.

Be aware of all the problems any of the 1542s can cause in today's
faster systems.. CPs were more problematic than the CF's for
example. Make sure the PNP is turned off.

However - a 1542 device is an ISA bus device - and consquently
transfers to/from that device will go at the speed of the ISA bus -
typicall 6-10MHz based on your motherboard. Far less than a
33MHz 4-byte wide PCI bus for example.

Your Exabyte will accept data at a far higher rate than that which
the 1542 can supply. So using the 1542 the tape drive will probably
write to tape, stop, backup, wait, write, stop, backup, wait, and
so on, as it writes faster than the data rate coming to it. This
could backups to the Exabyte slower than using a tape drive that is
more evenly matched to the 1542 that could stream, and old QIC for
example.

Exactly what 'fails' on backing up. It fails to backup? It fails to
verify? The system fails? More detail on 'fail' would help just a
bit. I think you'd be far better off getting something like a 6 2940
PCI used SCSI controller than something that dates back 5 to 6 years
before that.


-- 
Bill Vermillion -   bv @ wjv . com
From - Mon Aug 27 11:12:00 2001
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From: robertl@localhost.localdomain (Robert Lipe)
Newsgroups: comp.unix.sco.misc
Subject: Re: Can I use an Adaptec 1542CP in an SCO OpenServer 5.0.6 box?
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On Mon, 27 Aug 2001 12:37:37 GMT, Bill Vermillion <bill@wjv.com> wrote:

>However - a 1542 device is an ISA bus device - and consquently
>transfers to/from that device will go at the speed of the ISA bus -

As an additional form of horror, remember that ISA only has 24 address
lines.   This means its DMA can address memory only in the bottom 16Mb.
So if you have a destination or source that's above that, it actually
DMAs to a bounce buffer in that bottom 16Mb and then copies to the "real"
address.   (The order is reversed for outgoing data, of course.)  This 
requires additional memory and a copy of all data on any sensible 
machine.   This may or may not be a concern for you, but you should be 
aware that this combination will pretty much slap the host silly while 
doing this.

>bit. I think you'd be far better off getting something like a 6 2940
>PCI used SCSI controller than something that dates back 5 to 6 years
>before that.

Yep.

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