44 Storage Management with DB2 for OS/390
• The number of volumes in the Storage Group satisfies the volume count
• Accessibility requested
• Availability (dual copy or RAMAC) requested
• The volume was explicitly requested and guaranteed space is YES
• Sufficient free space to perform the allocation without exceeding the high
threshold
• Volumes fall within a pre-determined range of millisecond response times
based on the request
• The volume supports extended format if EXT=PREFERRED or REQUIRED is
requested in the data class
Candidates forsecondar y volumesare primar y volumesthat, in addition:
• Are at or above high threshold, or exceed high threshold following the
allocation.
• Are quiesced, or the Storage Group to which the volume belongs is quiesced.
• Did not meet the requested millis econd response time.
• Did not meet the accessibility request of standard or preferred.
• Did not meet the IART of greater than zero.
• Did not meet the availability request of standard or preferred.
When a Storage Group does not contain enough volumes to satisfy the volume
count, all volumesin the StorageG roup are flagged tertiary.Tertiary volumes are
onlyselected when thereare no pr imary or secondary volumes and the request is
for a non-VSAM non-GUARANTEED SPACErequest.
After the system selects the primary allocation volume,that volume's associated
Storage Group is used to select anyrem ainingvolumes requested.
5.3.4.2 Planning for Implementation
Iti simpor tant thatunique Storage Groups are used for production databases and
recovery data sets,because of their critical status. Appropriate groups should be
defined bythe storage administrator to prevent automatic migration (AUTO
MIGRATE),and automatic backup (AUTO BACKUP). Howevernon-production
databases should be considered for placement on standard primary volumes
(possibility shared with other data types), as their availability is nor mally not as
critical.
DB2all owsthe DBA to define a collection of volumes that DB2 uses to find space
for newdata set allocation, known as STOGROUPs. When converting DB2
databases to SMS, and DB2 STOGROUPs are used to manage DB2 database
data, one wayi s todes ignt he SMS Storage Groups so they are compatiblewith
existingSTOGROUP definitions.
Once the conversionis complete, it is recommended that SMS be used, rather
than DB2 to allocate databases. Toallow SMS control over volume selection,
define DB2 STOGROUPswith VOLUMES(*).