Date: Mon, 27 May 2002 06:02:23 -0700 From: Cy Schubert - CITS Open Systems Group <Cy.Schubert@uumail.gov.bc.ca> To: Kirk Strauser <kirk@strauser.com> Cc: freebsd-stable@FreeBSD.ORG Subject: Re: Hardware RAID vs vinum Message-ID: <200205271302.g4RD2Nr1099239@cwsys.cwsent.com> In-Reply-To: Message from Kirk Strauser <kirk@strauser.com> of "26 May 2002 22:52:33 CDT." <87r8jy9ri6.fsf@pooh.int>
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In message <87r8jy9ri6.fsf@pooh.int>, Kirk Strauser writes:
>
> At 2002-05-27T03:41:39Z, "Phil Rosenthal" <winter@villaweb.net> writes:
>
> > Is there any reason why a hardware raid would be better, am I missing out
> > on anything?
>
> In theory, a hardware RAID should give you better CPU utilization. After
> all, a seperate processor (or DSP, etc.) would be doing all of the work that
> your main CPU is currently doing. Furthermore, your CPU would be able to
> forget about all of the extra abstractions of Vinum, such as plexes,
> subdisks, and so on - the RAID could look like one single harddrive.
>
> In reality, I don't think that the RAID controllers would protect the CPU
> from nearly so much work, and I'm almost positive that your CPU will be
> orders of magnitude faster than the processor on the controllers.
I beg to differ. I don't have any experience with vinum, however I do
have experience with other products such as VxVM (Veritas Volume
Manager) and ODS (Online Disk Suite).
About three years ago a rumor was floating around the building that "NT
was faster than Solaris." The customer in this case had a Sparc Ultra
2 system using RAID 5 on ODS (software RAID 5). The application people
and the NT folks managed to prove that when the Oracle application was
run on an NT system using hardware RAID 5 (of course they didn't
mention the hardware RAID 5 part), it ran 37 times faster than on the
Sun system. Sun found out and quickly shipped an Ultra 2 with an A3500
array to prove that Sun was no slouch. It turned out that moving the
application to hardware RAID improved performance by 40 times. (In the
end the customer was not willing to spend the money on an A3500 array
so to this day the application still uses software RAID 5, but we've
not installed software RAID since then.)
Did we see a difference in CPU utilization? No. However ODS and VxVM
run below the kernel and cannot be measured by vmstat or sar, which is
different to how vinum works because it is part of the kernel.
The moral of the story: You get better mileage out of a hardware RAID
controller.
--
Cheers, Phone: 250-387-8437
Cy Schubert Fax: 250-387-5766
Team Leader, Sun/Alpha Team Email: Cy.Schubert@osg.gov.bc.ca
Open Systems Group, CITS
Ministry of Management Services
Province of BC
FreeBSD UNIX: cy@FreeBSD.org
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