Date: Tue, 26 Aug 2003 09:15:00 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: David Landgren <david@landgren.net> Cc: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: A DLT unit on /dev/sa0 is really slow Message-ID: <20030826141500.GH26367@dan.emsphone.com> In-Reply-To: <3F4B1761.8060807@landgren.net> References: <3F4B1761.8060807@landgren.net>
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In the last episode (Aug 26), David Landgren said: > I have an external DLT tape (a COMPAQ DLT VS 40/80 5133 according to > camcontrol). It seems glacially slow to me. Last night I backed up > many gigabytes of files from a remote machine over NFS. It took over > five hours to do it. My overworked Sun E-450 will do this in a shade > over three hours. > > What is more, the remote machine and my FreeBSD box have gigabit > Ethernet adapters, and both machines, as well as the switch they are > connected to all report 1000baseT full duplex. The sun, on the other > hand, is running 100baseT. > > When I run a "tar t" to list the contents of the archive, the output > is really slow. It's taken about half an hour so far to list the > first 50 or so files (and none are exceptionally big, 10Mb on > average). > > When I listen to the tape drive, I hear it start and stop frequently, > with lots of pauses. I would have expected it to spin continuously. > It is, after all, a *streaming* device. DLTs will only stream if they are fed data at a fast enough rate; otherwise they shoeshine. Try running with a 64k blocksize instead of tar's default 10k ( tar cb 128 ) . -- Dan Nelson dnelson@allantgroup.com
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