Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!amdahl!nsc!voder!lynx!m5
From: m5@lynx.UUCP (Mike McNally)
Newsgroups: comp.unix.wizards
Subject: Re: Accessing a VAX tape drive from a S
Message-ID: <4343@lynx.UUCP>
Date: 8 Sep 88 19:42:51 GMT
References: <711@auvax.UUCP> <43200035@uicsrd.csrd.uiuc.edu> <3463@phri.UUCP>
Reply-To: m5@lynx.UUCP (Mike McNally)
Organization: Lynx Real-Time Systems Inc, Campbell CA
Lines: 29

In article <3463@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>kai@uicsrd.csrd.uiuc.edu writes:
>> > When writing a local tape, each write() call produces one record.
>> 
>> Not true when a blocking factor > 1 is used.  Each write just adds a little
>> to a buffer, and when the buffer is full, THEN one physical record is
>> actually produced.

Clearly there's some confusion between what tar does internally and what
the OS does. 

>
>	Say what?  On any Unix system I've ever seen, each write(2) system
>call produces exactly one physical tape record.

Most cheap SCSI tape drives have a fixed blocksize, often 512 bytes.  No
matter how much the OS wants to write 10240-byte blocks, the tape will have
10 separate 512 byte blocks on it.








-- 
Mike McNally of Lynx Real-Time Systems

uucp: lynx!m5 (maybe pyramid!voder!lynx!m5 if lynx is unknown)