On Thu, Nov 17, 2005 at 03:56:36PM +0000, Stephen Borrill wrote:
> This might be just noise actually. I've noticed the performance plummets 
> at around 20G through the disk (80G) to around 11MB/s from much highers 
> speeds at either end. I think it could well be down to a duff disk (but 
> there are no errors in dmesg).

With modern disks, speeds are very different depending on the place of the
data on the disk:
pop# dd if=/dev/rwd0d of=/dev/null bs=64k count=1000
1000+0 records in
1000+0 records out
65536000 bytes transferred in 2.447 secs (26782182 bytes/sec)
pop# dd if=/dev/rwd0d of=/dev/null bs=64k count=1000 skip=300000
1000+0 records in
1000+0 records out
65536000 bytes transferred in 2.607 secs (25138473 bytes/sec)
pop# dd if=/dev/rwd0d of=/dev/null bs=64k count=1000 skip=500000
1000+0 records in
1000+0 records out
65536000 bytes transferred in 2.999 secs (21852617 bytes/sec)
pop# dd if=/dev/rwd0d of=/dev/null bs=64k count=1000 skip=600000
1000+0 records in
1000+0 records out
65536000 bytes transferred in 4.839 secs (13543294 bytes/sec)

This is a 40GB drive, so skip=600000 is near the end.

So it depends on how you did your tests (did you use rwd0d in both cases ?).

> 
> Once again, sorry for the noise.
> 
> On an on-thread note, installed xen with 3.0_BETA for the first time this 
> morning and it works brilliantly! Thanks to all concerned!
> 
> Can someone clarify the state of Xen 2.0 vs NetBSD 2.x and 3.0? I thought 
> that NetBSD 2.x supported Xen 1.2 and support for 2.0 was added in 3.0 and 
> -current (with support for 1.2 being dropped).

Yes, that's it.

> 
> However, there's xentools20-2.0.7 available as a binary package for 2.0, 
> so I'm confused. Perhaps some explanation should be added to the 
> (excellent) HOW-TO?

Ha, that's a mistake. The package's Makefile doesn't check the NetBSD
version, and xentools20 doens't need anything but python to
build, so it can be build on any NetBSD version supporting python.
But it won't be usefull on anything not i386, and anything < 3.0_BETA.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--