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Help Calculating IOPS.

I need a little help when trying to calulate available IOPS in a raid array. I have been looking at wmarrow's calculator (http://www.wmarow.com/strcalc/) and I am a little lost when it gets to read cache hit ratio and write cache hit ratio. With four 7200rpm sata 3.0 drives in a raid 10 I get between 227 and 23000 IOPS (at 70%/30% read/write ratio) depending on how I manipulate these two fields. How should I properly calculate these two fields?

I realize that in production I would want fast 15K SAS drives, and as many as possible, but this is for a lab environment and I do not have the budget for SAS drives. Just need to get an estimate of how many iops I will have to deal with so I don't overtax the box. It will be running vSphere Hypervisor 4.1.

Andrew Hancock (VMware vExpert PRO / EE Fellow/British Beekeeper)

let's turn this around how many do you need?

here are some previous discussions in EE about iops

https://www.experts-exchange.com/questions/26579092/IOPS-calculation.html

https://www.experts-exchange.com/questions/26104923/IOPS-question.html

https://www.experts-exchange.com/questions/22669077/IOPS-Calculator.html

https://www.experts-exchange.com/questions/26273948/IOPS-query.html

https://www.experts-exchange.com/questions/26594242/Identifying-my-IOPS-needs.html

SOLUTION

Gugro

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driskollt

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driskollt

Oops, sorry you wanted 70% read.

Anyway...

Total IOPS = (DriveIOPS * #Drives) / (ReadRatio + (RAIDWritePenalty * WriteRatio))
So.
246IOPS = (80 * 4) / (.7 + (2 * .3))

arstacey

ASKER

Ok, so with that in mind, a RAID 10 array of 8 Sata 7200rpm 1tb drives gives me roughly 4TB of storage and 426 IOPS. If a windows 7 desktop requires roughly 20 IOPS virtualized, then I should be able to run a Server 2008 Server Core running DC, File Shareing, DNS, and DHCP roles as well as at least 16 Win 7 desktops all virtualized under VMWare ESXi? The server will probably only have 1 quad core xeon processor, an e5620 2.4 Ghz with Hyperthreading, and at least 24GB Ram.

driskollt

You're probably fine. Especially if it's just a lab. If your lab doesn't have SLAs for response time/etc, then I wouldn't worry about it too much.

Since it's a lab, your write/read ratio is probably going to be more like .85/.15 which will give you a little better performance.

The fact you're using RAID10 with SATA for a random workload is a good idea as well.