Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!heights!jiro From: jiro@heights.cit.cornell.edu Newsgroups: comp.unix.wizards Subject: Re: Raw disk I/O (Performance on NeXT OD) Message-ID: <1990Feb18.012533.2540@heights.cit.cornell.edu> Date: 18 Feb 90 01:25:33 GMT Organization: Cornell Information Technologies, Workstation Resources, Ithaca, NY Lines: 44 >>In article , marc@focsys.uucp (Marc H. >>Morin) writes: >>> I am investigating using the raw disk interface to increase performance >>> of our application. The application is an imaging system, thus the I/O >>> consists of large data transfers to and from the disk. >>We were looking into this as well. After testing, we decided to >>continue to use >>the block device, since it was at least three times faster than the raw >>device. I concluded then that the block device was doing some disk access >>optimizations that the raw device wasn't doing. Also, using the block >>device has the added advantage that any new optimizations in the driver >>would automatically be used by the application. > >Under SunOS, at least, the raw device doesn't do read ahead. Some applications >consider this a feature, others a bug. To prove this, try >$ /bin/time dd if=/dev/rsd0a of=/dev/null bs=8k >$ /bin/time dd if=/dev/sd0a of=/dev/null bs=8k >--- >Larry McVoy, Sun Microsystems (415) 336-7627 ...!sun!lm or lm@sun.com On the NeXT with a floptical, the two above commands reveal interesting times: csh> /bin/time dd if=/dev/od0a of=/dev/null bs=8k <-- Block floptical 30492 Records <-- 240 megabytes 4188.9 real 1.8 user 2927.7 sys ^^^^^^ csh> /bin/time dd if=/dev/rod0a of=/dev/null bs=8k <-- Raw floptical 30492 Records 1320.9 real 2.0 user 51.2 sys ^^^^ On the NeXT, the raw device is overwhelmingly faster than the block device. What is this supposed to mean? Any relationship to the disk being an Optical? - Jiro Nakamura - NeXT Developer (Unregistered, Independent) ---------------------------------------------------------------- jiro@heights.cit.cornell.edu Disclaimer: I work for no-one.