From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Pearson Subject: LTO-3 read performance issues Date: Wed, 07 Nov 2007 15:18:05 +0000 Message-ID: <4731D72D.5000404@moving-picture.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mpc-26.sohonet.co.uk ([193.203.82.251]:57580 "EHLO moving-picture.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753934AbXKGPuW (ORCPT ); Wed, 7 Nov 2007 10:50:22 -0500 Received: from minion.mpc.local ([172.16.11.112] helo=moving-picture.com) by moving-picture.com with esmtp (Exim 4.43) id 1IpmfN-0005zD-NM for linux-scsi@vger.kernel.org; Wed, 07 Nov 2007 15:18:05 +0000 Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org I have two LTO-3 (QUANTUM ULTRIUM 3) drives attached to a dual Adaptec U160 controller (one per SCSI host) on a Dell PE2850 running a RHEL4 based kernel (2.6.9 based). I'm trying to read (with tar) LTO-3 tapes written on another system (possibly an SGI IRIX box), but I'm getting extremely variable read rates - from a few Kb/s to tens of Mb/s - while reading the same tape After a bit of trial and error, it looks like the tapes have been written in variable block mode with a block size of 16Kb To list the tapes, I need to set the block size to 0 (mt setblk 0) and run: tar tvfb $TAPE 32 Running strace on the tar process shows that it does a number of read()'s then 'sticks' on a read() for a number of seconds, and then does a burst of read()'s - the number of reads it does in these bursts and the time if waits on a particular read vary. My guess this is something to do the drive having to repositioning the tape between reads and breaking the tape streaming ... I get the same issue on both drives with different tapes from the same source. I am using the default st module options and not doing anything other than using 'mt setblk 0'. Is there anything I can do to get a decent, sustained read rate from these tapes? Thanks James Pearson