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Newsgroups: comp.os.386bsd.questions Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.Hawaii.Edu!ames!nic.hookup.net!news.kei.com!eff!usenet.ins.cwru.edu!news.csuohio.edu!stever From: stever@csuohio.edu (Steve Ratliff) Subject: Tar and wt driver, was: FreeBSD and Archive SC499 Message-ID: <1994Jan20.061425.27881@news.csuohio.edu> Sender: news@news.csuohio.edu (USENET News System) Organization: Cleveland State University X-Newsreader: Tin 1.1 PL5 Date: Thu, 20 Jan 1994 06:14:25 GMT Lines: 18 I've been tinkering around with why tar was so slow in backing up to the wt driver in FreeBSD. The conclusion that I have reached is that the default blocking size of 20 512byte blocks is way to small for tar to keep the tape drive streaming very well. It is actually painful to watch it grab 10K off the hdd and then write 10K to tape and rewind to update the tape header. On my system the magic incantation to get it to stream really well is: tar -cvb 512 -f /dev/rwt0 [filesystem_to_backup] The optimum blocking value may vary under system loading and from system to system. I would suggest that you start with "-b 64" and work your way up by powers of 2 until it streams well for you. I hope this saves some people the agony of a six hour backup of /usr/X386 that I endured before I figured this out. :)