geom stripe perfomance question

[Oles Hnatkevych <don_oles_(_at_)_able_(_dot_)_com_(_dot_)_ua>]

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 tried to do the same with gvinum/stripe - the read
speed was degraded too. And with gmirror depending on slice size speed
was degraded differently.


I am running 6.2-PRERELEASE on Celeron 800.



-- 
 Oles Hnatkevych                          mailto:don_oles_(_at_)_able_(_dot_)_com_(_dot_)_ua

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