Date: Sun, 5 Jul 1998 12:18:30 +0930 From: Greg Lehey <grog@lemis.com> To: Ustimenko Semen <semen@iclub.nsu.ru>, David Kelly <dkelly@hiwaay.net> Cc: Harlan Stenn <Harlan.Stenn@pfcs.com>, dc-sage@dc-sage.org, scsi@FreeBSD.ORG, amanda-users@cs.umd.edu Subject: Re: DDS/2 tape specs Message-ID: <19980705121830.B358@freebie.lemis.com> In-Reply-To: <Pine.BSF.3.96.980704152249.28181A-100000@iclub.nsu.ru>; from Ustimenko Semen on Sat, Jul 04, 1998 at 03:34:28PM %2B0700 References: <199807032016.PAA21647@nospam.hiwaay.net> <Pine.BSF.3.96.980704152249.28181A-100000@iclub.nsu.ru>
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On Saturday, 4 July 1998 at 15:34:28 +0700, Ustimenko Semen wrote: > On Fri, 3 Jul 1998, David Kelly wrote: >> Harlan Stenn writes: >>> My second test took 8191 `y' characters followed by a newline: >>> >>>> yes `cat 8ky` | dd bs=8k of=/dev/rst0 >>> >>> and I eventually killed after over 24 hours' elapsed time. >>> When I killed it, I think it claimed to have written nearly 10G to the tape. That's reasonable. You've chosen an almost ideal pattern for compression. >> 24 hrs for only 10G doesn't sound good. >> >> To a similar DDS-2 (with compression) drive I once used dd to copy >> /dev/null until something broke. Got 88G on a DDS-1 90m tape. Took >> about 8 hours. SGI Indy R5000, Irix 6.2, OEM SGI/Seagate/Archive DDS-2 >> tape drive. > > Yes, in good times it writes real fs data on 500-800 Kb/s. > But in worst, it goes on 20-80 Kb/s :-( > > Else total capacity and speed decrease after you use tape many > times without eraseing it and/or cleaning drive's head. No, the capacity stays the same. But if you don't clean the head, it'll have more and more soft errors, and the throughput will drop dramatically. > IMHO there are linear dependence between data speed and cartridge > capacity (becouse the tape speed is fixed). Tape speed is fixed, but that doesn't mean that it's moving all the time. If the drive gets a data underrun on write, it'll stop, back up, and start again. This can drop its speed by 95% or more. This will also happen on I/O errors. This is obviously what's been happening to you. > I'm useing SDT-7000 under 2.2.6-stable. And i can't say: > `It works perfectly!` :-( Not surprising. Greg -- See complete headers for address and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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