E20-324 VideoILT material questions - Performance Drives

Hi,

Please help me with the following questions.   Thank you and your help is much appreciated.

I have  questions on Module 4, at the bottom of page 28:

" Total performance drives Total Approximate Drives = RAID Group IOPS / (Hard Drive Type IOPS) + Large Random I/O adjustment

+ Hot Spares + System Drives

For example, if an application was previously calculated to execute 4,000 IOPS, the I/O is 16 KB random requests, and the hard drives specified for the group are 15K RPM SAS drives (see Table 9 Small block random I/O performance by drive type):

Total Approximate Drives = 4,000 / 180 + 0 + ((4,000 / 180) / 30) + 5

Total Approximate Drives = 28 "

From the formula above:

Raid Group IOPS / ( Hard Drive Type IOPS 0 = 4,000/180

Q1 . Large Random I/O adjustment = 0  (is this right ?)

Q2. What is ((4,000 / 180) / 30) ?  Why is (4000/180) divided by 30 ?  What is 30 ?

Q3. What is 5 ? 

Q4 .How many system or vault drives is required ?  4 ?

Q5. Is Raid 10 always configured for vault drives ?

Q6. In the earlier part of the page : " Do not include the system drives and hot spare drives into the performance calculation when calculating the operational performance "

Why is the hot spares and system drives included in the above formula ?