The first step for implementing class transition processing in
your environment is to determine which data sets would benefit from
this type of processing. Two possible candidates are:
- Data sets that are not eligible for migration because they always
need to reside on L0 storage. These data sets could be initially allocated
on a particular class of storage and then transitioned to a lower
class of storage using class transitions.
- Data sets that are currently eligible for migration in order to
reduce the cost of storing them, but would improve application performance
if they could be kept online. The management class for these data
sets could be changed such that instead of migrating the data after
a certain period of time, they are transitioned to lower cost L0 storage.
For example, say that you have Easy Tiers devices and SATA devices.
Data sets are initially allocated to an Easy Tiers device that provides
real time data placement on the appropriate storage tier based on
usage. You know that after 45 days, however, certain data set types
are rarely accessed and you do not want this set of data mixed with
your active data. This set of data could be assigned to a management
class that after 45 days will automatically move the data sets from
a storage group comprised of Easy Tiers devices to a storage group
comprised of just SATA devices.
The next step would be to update the SMS environment to support
class transitions:
- Storage devices with differing characteristics must be segregated
by storage class and storage group. For example, Easy Tiers devices
must be assigned to different storage groups than SATA devices. If
the devices are placed within the same storage groups, then SMS is
unable to distinguish the appropriate device that is desired. SSD
devices may reside within the same storage group since the storage
class can be used to specify that an SSD device is preferred over
another type of storage.
- ACS routines must be written for the new ACS environment SPMGCLTR.
Determine the actions you wish to occur for the class transition and
write the appropriate routine. For example, if you wish the class
transition to move the data set from an EASYTIER storage group to
a SATA storage group, you could define an ACS routine as seen in the "Storage Group:" section of Figure 1.
- Define or update management classes with the new class transition
characteristics. Remember that only the appropriate data set type
should be assigned to management classes with a SERIALIZATION EXIT
value other than NONE.
Note that no changes are required to the DFSMShsm space management
functions. They will automatically examine management classes for
the class transition settings and process data sets accordingly. If
you expect class transition processing to increase the amount of work
done during space management, then you may wish to increase the number
of tasks that are assigned to that processing.