From owner-freebsd-current Thu Dec 26 12:29:58 1996 Return-Path: Received: (from root@localhost) by freefall.freebsd.org (8.8.4/8.8.4) id MAA06215 for current-outgoing; Thu, 26 Dec 1996 12:29:58 -0800 (PST) Received: from alpo.whistle.com (alpo.whistle.com [207.76.204.38]) by freefall.freebsd.org (8.8.4/8.8.4) with ESMTP id MAA06210 for ; Thu, 26 Dec 1996 12:29:55 -0800 (PST) Received: from current1.whistle.com (current1.whistle.com [207.76.205.22]) by alpo.whistle.com (8.8.2/8.8.2) with SMTP id MAA29432; Thu, 26 Dec 1996 12:24:44 -0800 (PST) Message-ID: <32C2DECD.41C67EA6@whistle.com> Date: Thu, 26 Dec 1996 12:23:41 -0800 From: Julian Elischer Organization: Whistle Communications X-Mailer: Mozilla 3.0Gold (X11; I; FreeBSD 2.2-CURRENT i386) MIME-Version: 1.0 To: Joerg Wunsch CC: FreeBSD-current users Subject: Re: DAT: reading with blocksize=256K References: <199612261923.UAA27137@uriah.heep.sax.de> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-current@freebsd.org X-Loop: FreeBSD.org Precedence: bulk J Wunsch wrote: > > As Julian Elischer wrote: > > > the drive is in fixed block mode. > > in FIXED block mode what is actually written to tape is fixed blocks > > and many are written at a time for a large read/write > > But, you can't do 1 MB fixed blocks, right? :-) > no, but if you do a write of a 1MB block (e.g. dd bs=1M), physio will do 16 writes of 64K which will each be written as 64 x 1K blocks onto the media. This appears on tape as 1024 x 1K blocks which is indistinguishable from 1020 x 1K blocks written in one hit by (say) and SGI. and you can read the data back using (say) 4K reads in which case you'll get 4 1K blocks at each read, and you will get valid data for 256 reads.