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From: mcdowell@.exlog.com (Steve McDowell)
Newsgroups: comp.unix.wizards
Subject: Exabyte blocking (/dev/rst*)
Message-ID: <1991Jun14.161316.13848@exlog.com>
Date: 14 Jun 91 16:13:16 GMT
Sender: mcdowell@exlog.com (Steve McDowell)
Organization: Exploration Logging, Inc.
Lines: 23



I am running under Sun's version of UNIX. 

I have an exabyte tape that was recorded using a logical block size of 
1024 bytes. I have written some software to copy these things; the problem
is that the st SCSI tape driver only wants to read 1024 bytes -- actually it 
seems to perform up to 4 physical reads for a total of 4095 bytes for any given 
read request. This is simply unacceptable performance for this application.  

The Exabyte documentation shows a variable read mode that would allow for 
larger transfer sizes. The question is this: how do I make the "st" driver
utilize this feature and do reasonable reads? Is there an ioctl() option 
that isn't documented in the mt documentation? 




-- 
---------------------------------------------------------------
Steve McDowell			      Exploration Logging, Inc.
Software Engineering   
Opinions expressed are, of course, my own and not Exlog's.