A heat map is a workload activity metric that
is calculated for each extent in a logical volume. The workload activity
is expressed as a temperature gradient from hot (high activity) to
cold (low activity). Use of the heat map transfer utility requires
the Easy Tier® monitoring
function to be enabled at each of the primary and secondary storage
systems involved in the heat map transfer.
The heat map transfer utility periodically transfers Easy Tier heat map information from primary
to secondary storage systems. The secondary storage system generates
migration plans based on the heat map data and (the secondary storage
system's) current physical configuration. In this way, the performance
characteristics of the secondary storage are consistently updated
to reflect that of primary storage. Multiple secondary storage systems
are supported. Alternatively, you can have multiple primary storage
systems that are associated with a single secondary storage system.
It is recommended that the secondary storage system has the same physical
configuration as the primary storage system. Secondary storage systems
are then workload optimized based on primary storage system usage,
with no performance penalties if data recovery is necessary.
Note: Currently, the heat map transfer utility does not support
replicating tier assignment instructions of the Easy Tier Application from the primary
to secondary storage systems. To reflect the same tier assignment
on the secondary storage systems, issue the same tier assignment commands
on the secondary storage systems.
Data that occurs in the I/O cache layer (including the storage
and server-side cache) is not monitored by Easy Tier and not reflected in an Easy Tier heat map.
If a workload failover occurs, the secondary storage system:
- Uses the heat map data that is transferred from the primary storage
system.
- Maintains performance levels equivalent to the primary storage
system while the primary storage system is unavailable.
Note: Without the same physical configuration, a secondary storage
site is able to replicate the heat map data, but is unlikely to be
able to replicate the performance characteristics of the primary storage
system.
The heat map transfer utility runs either on a separate Windows or Linux host, or on Tivoli® Storage Productivity Center for Replication.
From the host, the heat map transfer utility accesses the primary
and secondary storage sites by using an out-of-band IP connection.
Transfer of heat map data occurs through the heat map transfer utility
host, as illustrated in
Figure 1.
Figure 1. Flow of heat map data
The heat map transfer utility imports the heat map data from the
primary storage system, and analyzes this data to:
- Identify those volumes that have a peer-to-peer remote client
(PPRC) relationship.
- Determine the type of PPRC relationship that exists. This can
be Metro Mirror, Global Copy, or Global Mirror.
The heat map information for the selected volumes is then periodically
copied from the primary storage system to the heat map transfer utility
host (default copy period is 12 hours). The heat-map-transfer utility
determines the target secondary storage system that is based on PPRC
volume mapping. The utility transfers the heat-map data to the associated
secondary storage systems. The heat-map data is then imported to the
secondary storage system, and Easy
Tier migration plans are generated based on the imported and
existing heat map. Finally, the result of the heat map transfer is
recorded (in memory and to a file).
To enable heat map transfer, the heat-map transfer-control switch
that is on the secondary storage system needs to be enabled
-ethmtmode
enabled. This is the default mode. Use the DSCLI command
chsi to
enable or disable heat map transfer:
chsi -ethmtmode enable | disable
The scope of heat map transfer is determined by the Easy Tier automatic mode setting:
- To automatically transfer the heat map data and manage data placement
for logical volumes in multi-tiered pools, use the Easy Tier control default settings (-etmonitor
automode, -etautomode tiered).
- To automatically transfer the heat map data and manage data placement
for logical volumes in all pools, use the Easy Tier control settings (-etmonitor
all, -etautomode all).
Note: For PPRC relationships by using Global Mirror, Easy Tier manages data placement
of the Global Copy target and FlashCopy® source
only, and does not manage data placement for a FlashCopy target that is involved in the
Global Mirror relationship.
If you do not have an Easy
Tier license, and want to run an Easy Tier evaluation on both the primary
and secondary storage systems, set the Easy Tier control on both storage systems
to "monitor only" (-etmonitor all). The heat map
transfer utility then automatically transfers the heat map data and
uses this data to generate an Easy
Tier report, without changing the data layout on either of the
storage systems.
