Date: 5 Sep 2000 02:53:33 +0200 From: naddy@mips.inka.de (Christian Weisgerber) To: freebsd-scsi@freebsd.org Subject: Re: Keeping a DLT4000 streaming? Message-ID: <8p1g6d$30f2$1@ganerc.mips.inka.de> References: <8oth09$u2b$1@ganerc.mips.inka.de> <Pine.BSF.4.21.0009031400140.90484-100000@mail.wolves.k12.mo.us>
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Chris Dillon <cdillon@wolves.k12.mo.us> wrote: > I keep my DDS drive streaming [...] by using several large 'team' > (ports/misc/team) buffers. I currently use five 8MB buffers. A > buffer only empties when it is full, so that way only 8MB streamable > chunks make it to the drive, even if the disks can't keep all of the > buffers full. You might want 32MB at a time or more for a DLT drive I've played around with this, and it just doesn't work. The team processes fill up their buffers at 8.0+MB/s, then they feed the data slowly at ~2.8MB/s or so to the tape drive. "iostat -d 1" shows that there are periods with no disk I/O at all. Apparently the team processes have filled their buffers and are waiting (while one is slowly feeding). I'm increasingly getting the impression that the DLT is simply not capable of accepting the data sufficiently fast from the SCSI bus. If the disk couldn't keep up with the tape, I would expect to see short bursts of maximum I/O on the tape bus (approaching 10MB/s), when a team process emptied its buffer. -- Christian "naddy" Weisgerber naddy@mips.inka.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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