--- On Tue, 31/3/09, Goswin von Brederlow <goswin-v-b@web.de> wrote:

From: Goswin von Brederlow <redacted>
Subject: Re: Adding more drives/saturating the bandwidth
To: Jon@eHardcastle.com
Cc: "Goswin von Brederlow" <redacted>, linux-raid@vger.kernel.org
Date: Tuesday, 31 March, 2009, 10:07 PM
Jon Hardcastle [off-list ref] writes:

quoted

--- On Mon, 30/3/09, Goswin von Brederlow

[off-list ref] wrote:

quoted

quoted

From: Goswin von Brederlow

[off-list ref]

quoted

quoted

Subject: Re: Adding more drives/saturating the

bandwidth

quoted

quoted

To: Jon@eHardcastle.com
Cc: linux-raid@vger.kernel.org
Date: Monday, 30 March, 2009, 4:40 PM
Jon Hardcastle [off-list ref]

writes:

quoted

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Hey guys, How do you know if your machine can

handle

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adding some more drives to it? How can you check

that there

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quoted

is enough BUS IO to handle extra sata cards and

also that

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the machine is powerful enough to support say an 8

drive

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raid 5...

A) Try & error.
B) look up the speed of the bus and half it. Any

bandwidth

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left?
   make sure the cpu isn't at 100% already as

well

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MfG
        Goswin

Cheers guys, I dont think CPU will be an issue as when

i looked yesterday whilst copying to my 6 drive raid 5 array
it was at ~10% (the only time i get access issues is when i
am smart checking all 6 discs and trying to stream a movie
of it at the same time!)

quoted

As for try and error... sounds scary as once I have

added a drive to the array I can undo the process! I suppose
I could add them as JBOD's and then thrash the hell out
of them.. whilst accessing the rest of the array... What
does halving the bus speed tell me in anycase?

Just see if you can get a decent bandwidth from each disk:

for i in /dev/sd?; do dd if=$i of=/dev/null bs=1M
count=10240 & done
iostat -k 10


Halving the bus speed gives you a reasonable low
expectation of how
much data you should be able to pull of the disks. If your
disks can't
even fill half the bus bandwidth you certainly can cope
with more
disks or something is seriously wrong.

MfG
        Goswin
--

Whoops! of course it isn't; sorry. it is presumably a read test thought rather than a read/write? Safe to do whilst the array is constructed?

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N: Jon Hardcastle
E: Jon@eHardcastle.com
'..Be fearful when others are greedy, and be greedy when others are fearful.'
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