Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!yunexus!hydroesm!jtsv16!geac!alias!imax!dave From: dave@imax.com (Dave Martindale) Newsgroups: comp.unix.admin Subject: Re: Dumping to an exabyte tape drive Message-ID: <1990Sep13.213148.22831@imax.com> Date: 13 Sep 90 21:31:48 GMT References: <439@cfa.HARVARD.EDU> Organization: Imax Systems Corporation, Oakville Canada Lines: 22 In article <439@cfa.HARVARD.EDU> wyatt@cfa.HARVARD.EDU (Bill Wyatt,OIR) writes: > >In any case, >choosing a blocking that's a multiple of 8k will mitigate this loss, so >I can't understand why a blocking factor of 126 (63k) is often recommended. >A blocking factor of 56k=112 should be better. Yes, a blocking factor of 8k should minimize part-track writes. But this only matters if, in fact, the host can't keep the tape supplied with data. The 8200 drive only writes 246 kb/sec, and the Berkeley-style multi-buffered "dump" can easily supply that when reading data from a decently fast disk when the system is otherwise not busy (typical of overnight dumps). If you're not worried about keeping up to the tape, then setting the blocksize to 126 gives you the largest writes that are still a multiple of 1k, which minimizes system overhead and time spent transferring stuff on the SCSI bus. The 8500 drive will change all this, since the transfer rate is twice as fast. But then, the track size is likely to be something other than 8K too.