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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!spool.mu.edu!uwm.edu!cs.utexas.edu!howland.erols.net!feed1.news.erols.com!news.idt.net!cdc2.cdc.net!news.texas.net!node2.frontiernet.net!not-for-mail From: dsf@node6.frontiernet.net (Dan Foster) Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: whats a good external SCSI tape? Date: 13 Nov 1996 18:58:46 -0500 Organization: Frontier Internet, A reliable part of your life Lines: 83 Message-ID: <56dnbm$nm8@node6.frontiernet.net> References: <DzHp5B.6Bt.G.nanguo@nanguo.chalmers.com.au> <55u1fv$cgg@baygull.rtd.com> <56472e$ft9@newsbr.eunet.fr> <564sur$2f3@baygull.rtd.com> NNTP-Posting-Host: node6.frontiernet.net In article <564sur$2f3@baygull.rtd.com>, Don Yuniskis <dgy@rtd.com> wrote: >Frederic MARAND <Frederic.Marand@osinet.fr> wrote: >>Some customers are interested by the performance numbers of the DLT, >>but don't want to buy an expensive product like Storage Manager. >>By the way, does someone have any performance numbers for DLTs under >>*BSD ? >Sorry, I haven't tracked this -- primarily since the box driving the >DLT is pretty clunky... :-( >>>>I know this is not a Netware forum, but I found none, and Novell's >>>>only answer is: this is an unsupported drive and it does not emulate a >>>>standard SCSI tape very successfully. How is it supported on FreeBSD ? >>>>Any specific changes to the standard SCSI tape driver ? Novell is *FULL OF SHIT* with that assertion. (No offense to the good folks at Novell who didn't make that assertion). In fact.. in one of the other data centers (a Netware shop), they're testing the exact same DLT library. We *require* good support... and it's not likely they'd have tested it if it was unsupported. If you need, email me and I'll put you in touch with the guy who's testing the DLT library in a Netware environment. It *IS* SCSI (well, all DLT models that I've ever seen, at least...). I use a single ended SCSI cable for a DLT4000 library with 10 tapes and robotics for the autoloader. (It's an Overland Data Inc. which uses the Quantum DLT4000 as its engine) What can I say... SCSI is SCSI. (Granted, there's lots of little gotcha's, but...) It's not FreeBSD or Netware, granted, but AIX sees it just fine as 'a generic SCSI device'. Tempted to test the library when I get my FreeBSD laptop back from the co-worker who has it home right now. After tweaking and talking with engineers on the phone at various manufacturers... what I've seen is that the best possible speed for a DLT4000 is about 1.5 MB/sec (ours peaked at 1.6 MB/sec but maintained around 1.4 MB/sec usually) when we set the variable blocksize to 0. I've heard from multiple sources that they've seen up to 10.6 MB/sec for a DLT7000 drive (this sounds suspiciously like the max compressed rate, though) A DLT7000 should be able to do up to 5 MB/sec natively, 10 MB/sec with hardware compression. Waiting 'til around March/April to buy one (by that time, bugs should be ironed out... mass release is around January, according to the senior Quantum rep I met with two days ago). For maximum performance for a DLT box, blocksize should be around 64K (tweak to find best value, but 64K is almost always the best), variable blocksize set to 0. More importantly, you might want to consider putting the DLT drive on its own SCSI bus/controller so you have a minimum of delays due to bus contention (remember, according to the SCSI protocol, various devices on the bus can fight/compete for attention). We threw it on a low end RS/6000 (ironic that the box is *much* smaller than the tape drive ;-) ) that has *zip* SCSI bus traffic (ie, nobody ever uses it) and that got the best performance (with the few tweaks). DAT vs DLT? Well... if you have a large amount of data you need to regularly back up, or want to recover from massive data loss ASAFP, DLT would be a better choice because it's faster and holds more overall (ie up to 70 gigs per CompacTape V tape as opposed to 8 GB for a 120 mm DAT tape). Up to 10 MB/sec for DLT, as opposed to about 700K/sec for DAT. There is one other factor, that I hadn't realized until I talked with a technician who repairs tape drives. He opened up 8mm and DLT tape drives. Basically, the tape path for an 8mm drive involves several pretty *sharp* curves, which leads to increased possibility of any one part breaking down and reducing useful lifetime -- of tape or parts, he didn't specify -- and is more of a pain to repair. DLT's, on the other hand, has a pretty simple tape path, easily fixing things like jammed tapes, and the tape drive can read DLT tapes faster - partly due to the inherent design of the tape path. In short, it depends on what your exact needs are. I use DAT for the smaller shops/networks, and DLT for the bigger ones (we're a nationwide ISP). On my home boxes, I use DAT because I rarely exceed 4 GB total anyhow, and am satisfied with it - fits my home computing needs quite well. Can't go wrong with DAT... just *NEVER* go with those cheap technologies like QIC (1/4")/ Travan tapes (too slow... cost per tape and number of tapes needed vs same thing with DAT makes DAT cheaper in the longer run... sometimes even just after the first full backup). Now, end of my DLT ravings'n'rantings. ;-) -Dan Foster Frontier Internet Internet: dsf@frontiernet.net