Date: Thu, 22 Apr 1999 12:01:12 -0700 (PWT) From: Matthew Jacob <mjacob@feral.com> To: Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de> Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: i/o error with larger QIC Message-ID: <Pine.LNX.4.04.9904221156160.317-100000@feral.com> In-Reply-To: <19990422203034.22930@uriah.heep.sax.de>
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> > write read speed using blocksize > blocksz speed f/512 f/1024 v/10K v/32K > ** > > v/32K 179K/s + + * 188K/s > v/10K 179K/s + + 190K/s (190K/s) > v/1024 104K/s + 137K/s (81K/s) (81K/s) > f/1024 179K/s ** ++ 133K/s 83K/s 82K/s > f/512 179K/s 87K/s 121K/s 191K/s 192K/s > > () Values in parenthesis are modi that are possible but not much > useful, since they return short blocks. > > + IO error > > ++ IO error plus ``Invalid request. Fixed block device requests must > be a multiple of 1 bytes'' (apparently some bug there) D'oh! That's a wierd one! > > * not useful, since only partial blocks would be retrieved, so > the remaining data in each block were lost; IMHO this should rather > yield an IO error instead (which it did in previous FreeBSD versions) > > ** blocksize currently needs to be manually adjusted back to 1024 > after each tape operation, since the driver resets it to 512 That's a bug to fix, yes. > > To summarize: > ------------- > > Variable-length logical blocks seem to work best, ever. You see- this is why this all has come to be a mess. *My* out of date experience with QIC had led me to believe that Variable && QIC was just not a good idea. I'm still not convinced of this (see other mail about what may be a design flaw)- but this is why I'm actually getting a QIC drive so I can assess, for myself (not out of manuals), what's going on. > Fixed-legnth blocks (either 512 or 1024 bytes) have problems with read > speed. This seems to be a driver problem, in particular since the > read speed using variable-length read operations is better. Given > that the best possible values are at best en par with the variable- > length recording values, i don't see why anybody would use fixed- > length mode. > > The driver seems to have bugs, see ++ and ** above. Btw., `mt stat' > reports compression 0x3 everywhere, although i know that only QIC-2GB > and above support compression at all. Maybe this is part of the > problem? > > Slow speeds above are accompanied by the tape going in `start-stop' > mode. > A more complete assessment than this will be performed soon. I don't think fixed mode is that great either, but I'm not convinced that variable mode with QIC drives is so fanatastic either. -matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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