Date: Tue, 03 Aug 1999 11:11:39 +0800 From: Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com> To: hackers@freebsd.org Cc: shocking@bandicoot.prth.tensor.pgs.com Subject: Adding disks -the pain. Also vinum Message-ID: <199908030311.LAA16741@ariadne.tensor.pgs.com>
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The people who I work for were about to junk a bunch of 6 year old disks when
I snaffled them. Among them were 4 DEC DSP5400S (3.8GB each), with a nice
external case. These disks had been doing duty on a boat carrying out seismic
surveys, attached to misc. Sun workstations. These are typical of their
vintage - full height 5 1/4" drives fast narrow SCSI2, and noisy as all
blazes. I have them hooked up to a NCR810, as one striped FS (it's just for
experiments, not valuable data). fdisking them was easy, but disklabelling
them was a royal pain. I ended up editing the /etc/disktab file to add an
appropriate label and running "disklabel -w -B /dev/rda0c DSP5400S" which
still gives an error message, but appears to install the label. I only found
out that it installed the label by accident, wasting a bunch of time in the
process.
I created a striped volume across the 4 drives with the default stripe size of
256K. I read the rather interesting discussion within the man pages about the
optimal stripe size and have a couple of queries. Firstly, the type of traffic
that this 13.9GB filesystem will see will be mainly sequential reading and
writing of large files. There will only be a few files (~2-30), each several
gigs. (I'm fooling around with the seismic software at home, and typcal
surveys can results in files many gigs in size). Given that FreeBSD breaks
I/Os down into 64k chunks, would having a 64k stripe size give more
parallelism? I'm seeing 4.4MB/s if I read from an individual disk, but only
about 5.6MB/s when reading from the striped volume. Looking at the systat
display, the 8k fs blocks do seem to be clustered into larger requests, so I'm
not too worried about the FS block size. What have people observed with trying
larger FS block sizes?
Stephen
--
The views expressed above are not those of PGS Tensor.
"We've heard that a million monkeys at a million keyboards could produce
the Complete Works of Shakespeare; now, thanks to the Internet, we know
this is not true." Robert Wilensky, University of California
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