Jon Hardcastle <jd_hardcastle@xxxxxxxxx> writes:
> --- On Mon, 30/3/09, Goswin von Brederlow <goswin-v-b@xxxxxx> wrote:
>
>> From: Goswin von Brederlow <goswin-v-b@xxxxxx>
>> Subject: Re: Adding more drives/saturating the bandwidth
>> To: Jon@xxxxxxxxxxxxxxx
>> Cc: linux-raid@xxxxxxxxxxxxxxx
>> Date: Monday, 30 March, 2009, 4:40 PM
>> Jon Hardcastle <jd_hardcastle@xxxxxxxxx> writes:
>>
>> > Hey guys, How do you know if your machine can handle
>> adding some more drives to it? How can you check that there
>> is enough BUS IO to handle extra sata cards and also that
>> the machine is powerful enough to support say an 8 drive
>> raid 5...
>>
>> A) Try & error.
>> B) look up the speed of the bus and half it. Any bandwidth
>> left?
>> make sure the cpu isn't at 100% already as well
>>
>> 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!)
>
> 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
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