HP XP P9500 Storage User Manual
Page 95
1.
Allocate pages and map them to THP V-VOLs
Pages are allocated and mapped to THP V-VOLs on an on-demand basis. Page allocation
occurs when a write is performed to an area of any THP V-VOL that does not already have a
page mapped to that location. Normally, a free page is selected for allocation from an upper
tier with a free page. If the capacity of the upper tier is insufficient for the allocation, the pages
are allocated to the nearest lower tier. A THP V-VOL set to a tier policy is assigned a new
page that is based on the tier policy setting. The relative tier for new page allocations can be
specified during operations to create and edit LDEVs. If the capacity of all the tiers is insufficient,
an error message is sent to the host.
2.
Gather I/O load information of each page
Performance monitoring gathers monitoring information of each page in a pool to determine
the physical I/O load per page in a pool. I/Os associated with page relocation, however,
are not counted.
3.
Create frequency distribution graph
The frequency distribution graph, which shows the relationship between I/O counts (I/O load)
and capacity (total number of pages), is created. You can use the View Tier Properties window
in Remote Web Console to view this graph. The vertical scale of the graph indicates ranges
of I/Os per hour and the horizontal scale indicates a capacity that received the I/O level.
Note that the horizontal scale is accumulative.
CAUTION:
When the number of I/Os is counted, the number of I/Os satisfied by cache hits
are not counted. Therefore, the number of I/Os counted by Performance Monitoring is different
from the number of I/Os from the host. The number of I/Os per hour is shown in the graph.
If the monitoring time is less than an hour, the number of I/Os shown in the graph might be
higher than the actual number of I/Os.
The following is an example of a frequency distribution graph.
Monitoring mode settings (see
) of Period or Continuous
influences the values shown on the performance graph. Period mode will report the most recent
completed monitor cycle I/O data on the performance graph. Continuous mode will report a
weighted average of I/O data that uses recent monitor cycle data, along with historical data
on the performance graph.
4.
Determine the tier range values
The page is allocated to the appropriate tier according to performance monitoring information.
The tier is determined as follows.
1.
Determine the tier boundary
The tier range value of a tier is calculated using the frequency distribution graph. This
acts as a boundary value that separates tiers
The pages of higher I/O load are allocated to the upper tier in sequence. Tier range is
defined as the lowest I/Os per hour (IOPH) value at which the total number of stored
pages matches the capacity of the target tier (less some buffer percentage) or the IOPH
value that will reach the maximum I/O load that the tier should process. The maximum
I/O load that should be targeted to a tier is the limit performance value, and the rate of
I/O to the limit performance value of a tier is called the performance utilization percent.
Smart Tiers
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