Very low disk performance on 5.x

[Arne Wörner]

--- Robert Watson <rwatson at FreeBSD.org> wrote:
> On Sat, 30 Apr 2005, Arne WXrner wrote:
> > 3. The man page geom(4) of R5.3 says "The GEOM framework
> >   provides an infrastructure in which "classes" can per-
> >   form transformations on disk I/O requests on their path
> >   from the upper kernel to the device drivers and back.
> >
> > Could it be, that geom slows something down (in some boxes the
> > reading 
> > ops are very slow; in my box the writing ops are very slow)?
> 
> [...]
> against a further offset region of ad0.  If they're against the
> same bits of disk, the main difference here will be the
> additional processing of the layers in the stack.  A little
> bit of math is required to figure out the offset, but dd
> should be usable to figure out the incremental  cost.
> 
I used the following commands:
1. dd if=/dev/ad0s2a bs=16k count=10000 of=/dev/null
2. dd if=/dev/ad0 iseek=2100357 bs=16k count=10000 of=/dev/null
(I think I did the math correctly; indeed the read speed of my ad0
varies between 45MB/sec (iseek=0) and 25MB/sec (in the end) with
bs=128k).
The results were nearly the same (both between 26MB/sec and
28MB/sec). Maybe I should have done it in single user mode.

My other hard disc ad1 (it is newer and bigger and faster and more
furious) behaves better (but I can just try writing via the file
system (ufs+s) and a final sync): The sync just needs .24sec of
18.28 seconds; the read and write speed is nearly the same (about
37MB/sec+/-1MB/sec).

Is there anything else, that could help to find the reason for the
difference between ad0's speed in R4.11 and R5.3?

-Arne


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com