Fwd: Abyssmal dump cache efficiency

[Zaphod Beeblebrox]

(oops... didn't group reply)

---------- Forwarded message ----------
From: Zaphod Beeblebrox <zbeeble at gmail.com>
Date: Feb 20, 2007 2:46 AM
Subject: Re: Abyssmal dump cache efficiency
To: Peter Jeremy <peterjeremy at optushome.com.au>

On 2/17/07, Peter Jeremy <peterjeremy at optushome.com.au> wrote:
>
>
> I've tried modelling a unified cache along the NetBSD line and there
> appears to be a massive improvement in cache performance.  It's unclear
> how much of an improvement this will give in overall performance but
> not physically reading data from disk must be faster than reading it.
>
> I believe it would be worthwhile creating a todo item to investigate
> this more thoroughly.


This squares perfectly with my recent observation that while runing some
combination of "dump | restore" that the dump disks incur 2 to 3 times more
I/O (reading) than the restore disks.  Now... for "performance" I was using
the cache function --- maybe the cache is actually a detriment.