Subject: Re: AlphaStation 255
To: None <Riccardo.Veraldi@fi.infn.it>
From: Robert Elz <kre@munnari.OZ.AU>
Date: 04/25/2001 23:25:20
Date: Wed, 25 Apr 2001 17:07:56 +0200 (CEST)
| I installed a IBM DNES 18GB and when I installed the system the default
| block size and frag size of 80192 amd 1024 where not fine in my case.
Something is wrong with your disklabel - perhaps you have defined tracks
that are way too huge, or something odd like that. The cyls/tracks/sectors
numbers aren't used for anything much related to any modern drive,
but they can make a huge difference to the way the filesystem works.
Find numbers that multiply as close as possible to the size of the drive
(but less or equal, not more), where sectors/track is of the general order
of 64 (something between 32 and 80), and tracks/cylinder is of the order
of 20 (10-24 is generally good). Those numbers match the general layout
style of the SMD drives from which all of this was originally designed.
For what it is worth, "factor" is an incredibly useful program for
calculating this stuff. Eg: if you have a drive with 11733120 sectors,
factor will produce 2 2 2 2 2 2 2 3 3 3 5 7 97 as the prime number factors.
From that, sects/track=64 (2^6) tracks/cyl=18 (2*3*3) cylinders=10185
(3*5*7*97) would be a nice layout to try. (64 * 18 * 10185 == 11733120)
On an i386 you have to be concerned with the stupid bios limitations
(so tend to have 63 sects/track, 15 heads (tracks/cyl) etc) - but on
an alpha there is no suck stupidity to bother with, so just make the
nicest numbers that fit.
If factor produces just a few large numbers as factors, then try again
with a number a few smaller (making it be a multiple of 128 is generally
good where possible, or 64).