# Calculating RAID Corrected IOPS

Member Posts: 32 ■■□□□□□□□□
Merry Christmas to everyone! I am currently studying for the EMCISA certification and I am using "Information Storage and Management: Storing, Managing, and Protecting Digital Information in Classic, Virtualized, and Cloud Environments" as my study guide.

I have a question regarding the chapter 3 question 6 exercise. It reads as follows:

"6. An application has 1,000 heavy users at a peak of 2 IOPS each and 2,000 typical users at a peak of 1 IOPS each. It is estimated that the application also experiences an overhead of 20 percent for other workloads. The read/write ratio for the application is 2:1. Calculate the RAID corrected IOPS for RAID 1/0, RAID 5, and RAID 6."

I understand that the total IOPS is 4800 and I understand that I need to know the write penalty of RAID 1/0 (2), RAID 5 (4), and RAID 6 (6). The formula given by the author to calculate RAID corrected IOPS is this:

% reads (IOPS) + write penalty (% writes X IOPS)

The question specifies that the read/write ratio for the application is 2:1 (but the study guide doesn't appear to cover that information). Did I miss something?

If I put that information into the formula for RAID 5 I get the following:

0.66 (4800) + 4 (0.33 X 4800) = 9504

Is this correct? I am having difficulty with this question because I believe that the read/write ratio corresponds to the % reads and % writes BUT these percentages are not whole numbers (if you divide 100/3 you get 33.3).

What information am I missing? I can't seem to wrap my mind around this.

Is there a different formula I should be using?

Any help is much appreciated!

## Comments

• Member Posts: 3,139 ■■■■■■□□□□
No you're fine.

The reads will always account for 3168 IOPS based on the above numbers, while the writes will vary based on the RAID penalty (3168, 6336, or 9504 respectively). So yes your total IOPS for RAID5 is correct 9504 (6336 for R1/0 and 12,672 for R6).
• Registered Users Posts: 1 ■□□□□□□□□□
Hi, I have to solve this problem:
The system, that operates with 64KB blocks has 1,000 heavy users at a peak of 2 IOPS each and 2,000
typical users at a peak of 1 IOPS each with a read/write ratio of 2:1. It is
estimated that the application also experiences an overhead of 20 percent
for other workloads. Heavy users have 400 GB and typical users have 75 Gb of unique data in this system. Calculate the IOPS requirements for RAID 1,
RAID 5, and RAID 6. Is it the same? Those 64 KB, 4000 GB and 75 GB are confusing.
• Registered Users Posts: 1 ■□□□□□□□□□
In the question it is mentioned that-
( the application experiences an overhead of 20 percent for other workloads.)
What does it means???
In above solutions we haven't use this value nywhere...
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