While you can globally enable or disable dynamic alias management
on the WLM ISPF panel, you can also individually enable or disable
dynamic alias management on a given device via HCD. You can do this
by specifying WLMPAV=YES or NO in
that device's HCD definition.
Note, however, that there is no consistency checking for dynamic
alias management between different systems in a sysplex. If at least
one system in the sysplex specifies WLMPAV=YES for
a device, then dynamic alias tuning will be enabled on that device
for all systems in the sysplex, even if other systems have
specified WLMPAV=NO. It is recommended not to
use dynamic alias management for a device unless all systems sharing
that device have dynamic alias management enabled. Otherwise, WLM
will be attempting to manage alias assignments without taking into
account the activity from the non-participating systems.
Note, also, that you can specify
WLMPAV=YES or
NO on both base and alias devices. The WLMPAV settings on an alias
device, however, is only meaningful when the alias device is bound
to a base device that is offline, as follows:
- If the base device is offline, then only alias devices
with WLMPAV set to YES will be reassigned to other
base devices.
The WLMPAV setting on the base device itself is irrelevant
when the base device is offline, for either “giving” or “receiving”
aliases. (Even if WLMPAV was set to YES on the base
device, it cannot have new aliases assigned to it, as it is offline.)
- For any base device that is offline to one or more systems in
the sysplex and online to others, the WLMPAV keyword in HCD needs
to be set to NO for the base device and its aliases.
You need to statically assign the desired number of aliases for the
base device via the ESS Specialist. If you try to use dynamic alias
management for such a device, WLM will make unpredictable alias moves.
- If the base device is online, then the WLMPAV settings
on the aliases are ignored, as follows:
- If WLMPAV is set to YES on the base device, then
the aliases can be reassigned regardless of their WLMPAV settings.
- If WLMPAV is set to NO on the base device, then
no aliases can be reassigned, regardless of their WLMPAV settings.
For a
WLMPAV=YES base device, the aliases initially
assigned to it should be allowed to default to
YES.
The only situation where you might want to change an alias to
WLMPAV=NO is
if the alias is initially assigned to a
WLMPAV=NO base
device. Because the base is set to
NO, the aliases
initially assigned to it will not be moved to other bases by WLM.
Then, because the aliases are set to
NO, if the base
is ever varied offline, the aliases remain assigned to that base and
cannot be reassigned by WLM to other bases. Certain combinations of
WLMPAV settings are not recommended, as described in table
Table 1:
Table 1. Effects of WLMPAV s ettings on base and alias devices| Base device WLMPAV setting |
Alias device WLMPAV setting |
Effects / recommendations |
|---|
| YES |
YES |
- If base is online: Base is WLM-managed. Aliases can be
freely moved to and from the base device by WLM.
- If base is offline: Aliases become unbound and are available
to WLM to assign to other WLM-managed bases.
|
| YES |
NO |
Not recommended. If base is
WLM-managed, then it is not predictable which aliases will remain
bound to that base when the base goes offline. If the base device
is set to YES, then you should set the aliases to YES as well. (See
previous option.) |
| NO |
YES |
Not recommended. If the base
is not WLM-managed, then you risk losing all of its aliases when the
device goes offline. (See next option.) |
| NO |
NO |
- If base is online: Base is not WLM-managed. The initial
aliases assigned to this base remain there.
- If base is offline: Aliases remain bound to the offline
base device and are not available to WLM for reassignment. When the
base comes back online, it retains its initial alias assignments.
|
In order for dynamic alias management to be most effective, you
should try to spread out your aliases in the initial definition. If
one base device has several alias devices while other base devices
have none, it will take more time for WLM to reassign the aliases
appropriately. Ideally, you should have at least two aliases assigned
to each base at the outset.
For more information about HCD definitions, see z/OS HCD Planning..