Re: Bad performance of virtual disk driver

[jdev%panix.com@localhost (Jed Davis)]

A long time ago, in article <20050503133455.GA3220%colwyn.zhadum.de@localhost>,
Matthias Scheler  <tron%zhadum.de@localhost> wrote:
> 
> The performace of the virtual disks is very bad ...
> 
>       # dd if=/dev/xbd1b of=/dev/null bs=1024k
>       512+0 records in
>       512+0 records out
>       536870912 bytes transferred in 331.800 secs (1618055 bytes/sec)
> 
> ... compared to the performance in the Linux dom0:
> 
>       # dd if=/dev/vg/matthias-1swap of=/dev/null bs=1024k
>       512+0 records in
>       512+0 records out
>       536870912 bytes transferred in 15.469114 seconds (34705990 bytes/sec)
> 
> Has anybody else observered this problem?

I have, in fact.  I think you'll find (with e.g. iostat) that NetBSD is
making fairly small disk requests (2k, I think it was?) when you read
from the block device, regardless of the size of the read().  Try dd'ing
from the raw device (e.g. /dev/rxbd1b) instead.

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