HP XP P9500 Storage - Manual (Page 22)

To measure write-workload and IOPS
1. Using your performance monitoring software, collect the following:
•
Disk-write bytes-per-second (MB/s) for every physical volume that will be replicated.
•
Data should be collected over a 3 or 4-week period to cover a normal, full business cycle.
•
Data should be collected at 5 minute intervals. If you use averages, shorter intervals
provide more accuracy.
2. At the end of the collection period, convert the data to MB/second, if needed, and import
into a spreadsheet tool.
Sizing journal volumes
Determining the required journal volume capacity
The following factors determine the required journal volume capacity:
•
The period of time during which data transfer can occur between hosts and the primary storage
system when there is a temporary increase in transferred data or a communication path fails
between the primary storage system and secondary storage system.
•
The data transfer speed for the period of time noted above.
To determine the journal volume capacity, use the following formula:
Formula 1: Journal volume capacity > (V H-M - V M-R ) × t
where:
•
V
H-M is the data transfer speed between hosts and the primary storage system.
•
V
M-R is the data transfer speed between the primary storage system and secondary storage
system.
•
t is the length of time during which data transfer can occur.
To calculate the journal volume capacity required when a communication path fails between the
primary storage system and secondary storage system, specify zero (0) for V
M-R .
The total capacity of journal volumes in each journal group must exceed the value in formula 1.
When data in the primary data volume of the Continuous Access Journal delta resync pair is
updated, if the journal data that exceeds 70% of the journal volume capacity on the primary site
of the Continuous Access Journal delta resync pair, the delta resync operation will fail. Therefore,
specify the larger value for the journal volume capacity on the primary site of the Continuous Access
Journal delta resync pair by comparing the values of formula 1 and formula 2.
Formula 2: Journal volume capacity > (V × t) × 1.5
where:
•
V is the data transfer speed between a host and the primary storage system.
•
t is the length of time until the delta resync operation starts.
CAUTION: The recommended journal volume capacity is 6 GB or more. If the capacity is less
than 6 GB, system performance may decrease due to the following:
•
The new data cannot be stored because the journal volume is full.
•
The performance of the initial copy decreases because the journal volume is full.
•
The journal group is suspended because the journal volume is full.
•
The indication of Usage Monitor is invalid.
22 Planning volumes and systems