Rule Of Thumb Calculation - Hitachi MK-97DF8018-00 User Manual

5. Calculate the base data pool size for your primary/virtual volumes by
multiplying the MB size of one V-VOL in Step
which was established earlier. For example:
90,000 MB
This is the base data pool size for a SnapShot system in which the copy
frequency is 1 hour, the copy lifespan is 4 hours, and the number of
copies (V-VOLs) is 4.
6. It is highly recommended that a safety factor of 20%, be calculated. Do
so using the following formula:
(Base data pool size) x 1.2. For example:
360,000 MB x 1.2 = 432,000 MB
7. It is also advisable to factor in annual increases in data transactions. Do
this by multiplying the base pool size by the percentage of expected
annual growth. For example:
432,000 MB x 1.2 (20 percent growth rate for per year)
= 518,400 MB
This is the size of the data pool with growth factored for the first year.
8. Repeat this step for each year the solution will be in place. For example:
518, 400 MB x 1.2 (20 percent growth rate for second year)
= 622,080 MB
This is the size of the data pool with growth factored for the second year.

Rule of Thumb Calculation

When measurements of host workload has not been performed, Hitachi
suggests the change rates shown in
•
Table 2-1: Workload Rates when No Measurement
Snapshot lifespan
1-4 hours
4-8 hours
8-12 hours
12-24 hours
Data pool calculation using the suggested change rates in
Data Pool size = (P-VOL x % of changed data x 2.5 safety rate)
x a number of V-VOLs
For example:
1. P-VOL = 1 TB. 1 snapshot per 24 hours. 25% of 1 TB = 250 GB.
2. Multiply the initial calculation by the Hitachi safety factor of 2.5. In the
example above: 2.5 x 250 GB = 625 GB. This is the base data pool size.
2–8
Hitachi Simple Modular Storage Copy-on-Write SnapShot User's Guide
x 4 V-VOLS = 360,000 MB
Suggested write workload
10%
15%
20%
25%
Planning and Design
4 by the number of V-VOLs,
Table 2-1.
change rate
Table 2-1 is: