vinum performance

[Lukas Ertl]

On Sun, 30 Mar 2003, Chuck Swiger wrote:

> Lukas Ertl wrote:
> [ ... ]
> > I created several RAID 0 and RAID 5 volumes with different stripe sizes
> > and let bonnie++ run over the filesystems. I was quite disappointed about
> > the RAID 5 performance, and even the RAID 0 performance wasn't too good
> > (a plain single disk filesystem was almost as fast as or even faster than
> > a RAID 0 stripe, and I wouldn't expect that).
> >
> > RAID 5 performance was really a mess, some of the test took more than
> > 30min. to complete.
>
> There are three goals or priorities to choose from when configuring
> RAID: performance, reliability, and cost.  What are yours?

I just wanted to test the performance of these drives and of vinum; I had
no goals to reach.

> Also, what tasks you intend to use the RAID filesystem for are critical
> to consider, even if the answer is simply "undifferentiated
> general-purpose storage".  In particular, RAID-5 write performance is
> going to be slow, even with RAID hardware support which offloads the
> parity calculations from the system CPU(s).  RAID-5 is best suited for
> read-mostly or read-only volumes, where you value cost more than
> performance.

Ok. But I still don't understand why RAID 5 write performance is _so_ bad.
The CPU is not the bottle neck, it's rather bored. And I don't understand
why RAID 0 doesn't give a big boost at all. Is the ahc driver known to be
slow?

> Um, that is a dual-channel card, and you're splitting drives onto both
> channels, right?

Yes, it is dual channel, but the disks I'm testing are all connected to
the same channel. Bad layout?

regards,
le

-- 
Lukas Ertl                             eMail: l.ertl at univie.ac.at
UNIX-Systemadministrator               Tel.:  (+43 1) 4277-14073
Zentraler Informatikdienst (ZID)       Fax.:  (+43 1) 4277-9140
der Universität Wien                   http://mailbox.univie.ac.at/~le/