mkfs and disk performance

[Daniel A. Graifer]

In article <1990Aug21.050638.15737 at cimcor.mn.org> det at cimcor.mn.org (Derek Terveer) writes:
>
>I believe that he gap is the interleave on your drive.  
>

I believe this is incorrect.  The interleave is the physical numbering
modulus for sectors on your drive.  This a function of drive controller/
format.

The 'gap' is parameter of the file system, and tells the file system how
to map 'contiguous' logical blocks of filespace to physical blocks.  Since
the standard file system buffers reads one block at a time, proper
gapping will cause a set of sequential reads to synchonize efficiently
with the availability of physical blocks on the drive.

Some of the newer 'fast file systems' do 'Block Bundled I/O (BBIO)'.  Our
vendor (Prime Computer) added this, and had us re-mkfs all of our partitions
with gap 1.  On files opened for sequential read, the file system attempts to
cache multiple blocks whenever a physical read occurs, which will only 
speed things up if sequential blocks of the file can be loaded in a single
contiguous read.

Our system was delivered with a number of utilites in /usr/lbin which the
system administration menus use to determine the cyl/gap parameters.  The
program that has been distributed on the net 'fsanalyze' (We got our copy
off of uunet) will tell you more about how your file systems are structured.

All of the above is my interpretation of the manuals combined with comments
from Prime, and examining fsanalyze output.  I make no guarantees about the
accuracy of my comments.

Dan
-- 
Daniel A. Graifer			Franklin Mortgage Capital Corporation
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