Subject: Re: slow disk access with large cpg values
To: Lubos Vrbka <shnek@tiscali.cz>
From: David Laight <david@l8s.co.uk>
List: netbsd-users
Date: 04/21/2004 21:04:01
> i observed that whereas the older one uses cpg=86 the new one has 
> cpg=28456

The 'cpg' field of the disklabel no longer contains the number of cylinders
in a cylinder group.  The filesystems 'cylinder groups' are no longer
aligned to physical cylinders, and the filesystem data areas are defined
as if there were a single cylinder in each group.

Because the allocation bitmaps for a cg have to fit inside a fs block,
with 8k blocks (the default) each cg has a maximum size of (about) 55MB.
This means that large (ie any modern) disk has a lot of cylinder groups.

	David

-- 
David Laight: david@l8s.co.uk