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Re: realtime section bugs still around

To: stan@xxxxxxxxxxxxxxxxx
Subject: Re: realtime section bugs still around
From: Jason Newton <nevion@xxxxxxxxx>
Date: Tue, 31 Jul 2012 22:55:54 -0700
Cc: xfs@xxxxxxxxxxx
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On Tue, Jul 31, 2012 at 8:55 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:

Intel Matrix RAID is fakeraid.  Designed for consumer workloads.  You're
shoving a decidedly non consumer, high b/w IO stream through it.  Don't
expect much.  In fact I'm surprised you're using consumer grade gear for
this application.  You are designing this software/system for a
commercial use case, correct?  If so I'd get some better hardware.

CPU overhead for fakeraid will be similar to md/RAID, depending on the
vendor and implementation.  In some cases it may be much higher than md.

I see.  Its important things stay COTS and small... things are sort of in a prototyping phase with some size and power constraints.  We had problems packaging what we already have and consider we already have some specialized io hardware we've had to account for..  There's just not much if any room available anymore.  We're getting refined tasks in the future and requirements will change as well... in particular this disk streaming component is perhaps a one-off  thing that we were notified of late in the game.

I did read around that from intel sources that Matrix Storage it really more of a hybrid solution... after all, they make sata controllers... and they already have to put up with 6Gb/s in hardware. But maybe they save a penny on the real-estate.. so maybe it's just fluff from intel PR.  What kind of hardware do you need in addition to make hardware raid 0 or 1 though.... .

> 2.  ATA overhead
>> 3.  IRQ/MSI overhead
>> 4.  Etc.
>> All these small bits add up to more than negligible CPU overhead at high
>> data rates.
> Regarding the others, how would I go about measuring their overhead...

To what end?

Just to figure out for sure what the bottlenecks are and whether they can be dealt with rather than looking at it as opaque system and assuming nothing can be done.  Also as a learning experience.


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