geom stripe perfomance question

[Pawel Jakub Dawidek]

On Sat, Nov 04, 2006 at 10:28:57PM +0200, Oles Hnatkevych wrote:
> Hello all!
> 
> I wonder why geom stripe works much worse than the separate disks that
> constitute stripe.
> 
> I have a stripe from two disks. Disks are on separate ATA channels.
> 
> root# gstripe list
> Geom name: bigdata
> State: UP
> Status: Total=2, Online=2
> Type: AUTOMATIC
> Stripesize: 262144
> ID: 4233231544
> Providers:
> 1. Name: stripe/bigdata
>    Mediasize: 500118323200 (466G)
>    Sectorsize: 512
>    Mode: r1w1e1
> Consumers:
> 1. Name: ad1
>    Mediasize: 250059350016 (233G)
>    Sectorsize: 512
>    Mode: r1w1e2
>    Number: 0
> 2. Name: ad2
>    Mediasize: 250059350016 (233G)
>    Sectorsize: 512
>    Mode: r1w1e2
>    Number: 1
> 
> Now let's read one of them and stripe.
> 
> root# dd if=/dev/ad1 of=/dev/null bs=1m count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes transferred in 14.579483 secs (71921343 bytes/sec)
> 
> root# dd if=/dev/stripe/bigdata of=/dev/null bs=1m count=1000
> 1000+0 records in
> 1000+0 records out
> 1048576000 bytes transferred in 15.882796 secs (66019610 bytes/sec)
> 
> What I would expect is doubling the speed of transfer, not
> slowing down. Am I wrong? Or is geom_stripe inefficient?
> 
> I am running 6.2-PRERELEASE on Celeron 800.

It should be, but first try something like:

dd if=/dev/ad1 of=/dev/null bs=1m count=1000 &; dd if=/dev/ad2 of=/dev/null bs=1m count=1000 &

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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