Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!aber-cs!rupert!pcg From: pcg@rupert.cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.unix.xenix Subject: Re: ESIX vs. SCO Xenix Message-ID: Date: 26 Mar 90 15:56:02 GMT References: <1826@crash.cts.com> <228@bradf.UUCP> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 35 In-reply-to: brad@bradf.UUCP's message of 15 Mar 90 05:48:53 GMT Posting-Front-End: GNU Emacs 18.47.1 of Wed Mar 15 1989 on rupert (berkeley-unix) In article <228@bradf.UUCP> brad@bradf.UUCP (Bradley W. Fisher) writes: There is one aspect of the *NIX wars that I haven't seen discussed yet ... one that I consider to be of the utmost importance ... how long does it take to back/restore from tape? So far comparing SCO, Altos, NCR, and Interacive , SCO wins hands down! Typically, 80 megabytes will stream to tape in about 40 minutes under SCO with a standard Wangtek 5099EN tape drive and PC-36 controller. The same amount of data and tape system takes about 3 hours under Interactive. Altos and NCR are slightly faster than 386ix, but *nobody* beats SCO in this respect from what I've seen. Why is this? The reason is that you are not using any of them properly, and SCO uses a dirty and potentially dangerous trick. In order to make the tape stream, you have to overlap disc reads with tape writes (or viceversa). When the tape streams, it will take less than 20 Minutes to dump 80 megs, not 40 as you are getting. To overlap disc and tape IO you need buffering and two processes or more. Try using my own 'team', posted to alt.sources, or 'ddd', posted to comp.sources.misc, as tape writing filters. Also, try using GNU tar or pax or afio instead of dump; they are more portable and often faster, even if admittedly dump/restor is faster on restore... The trick that SCO uses is to make the tape driver grab a tape buffer from the filesystem buffer cache, and then write this asynchronously to the tape device. This sort of works, but does not provide sufficient overlap, and completely alters the semantics of raw device writes. The bottom line is that with the right tools you get 4-5 megs per minute on any UNIX system that has enough filesystem read bandwidth and a QIC tape. -- Piercarlo "Peter" Grandi | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcvax!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk