Open System Services Management and Operations Guide (G06.30+, H06.08+, J06.03+)

listed in the storage-pool file can be viewed as the creation pool, a subset of the entire storage
pool used by the fileset. Figure 11 (page 89) shows the difference between an OSS storage pool
and the contents of the storage-pool file for the fileset DATA5; the creation pool is enclosed in a
rectangle to indicate that it is the set of disk volumes identified in the storage-pool file.
The OSS name server for a fileset uses the storage-pool file for that fileset to determine where to
create each new OSS data file. When that OSS name server receives a file-creation request, the
server reads the storage-pool file and creates the file on the disk volume whose name appears in
the storage-pool file following the volume name used for the last request.
As each new file is created, the fileset’s OSS name server continues along the list of volume names,
selecting a new volume with each request. The OSS name server ultimately wraps around to the
beginning of the list in a round-robin fashion.
Thus, if users write only small files in one disk volume in the list and only large files in another,
then one volume can fill up before the others. By allocating a large enough fileset, you can help
avoid the problems produced by this unlikely file distribution.
An OSS name server cannot allocate files on more than 20 disk volumes for one fileset. However,
each time a fileset is mounted, you can specify either:
• A different set of disk volumes for the creation pool of the fileset (different content of the same
storage-pool file)
• A different storage-pool file for the fileset, containing a different set of disk volumes
As a result, a fileset can span many disk volumes. OSS files can exist on disk volumes that are part
of the fileset even though they are not in any active storage-pool file. The storage pool for the fileset
can be much larger than the creation pool defined by the content of the storage-pool file.
For this reason, a storage-pool file cannot contain more than 20 active volume names (the creation
pool) but the volume list maintained by an OSS name server for the fileset (the entire storage pool)
can contain up to 256 disk volumes. See “FSCK Log File” (page 160) for more information about
the volume list.
You should not set up a fileset to use a disk volume that is not always in the storage-pool file for
that fileset. Normal operating procedures for a fileset can have unplanned side effects on the OSS
files on such disk volumes. See “Changing the Physical Makeup of a Fileset” (page 157) for more
information.
88 Understanding the OSS File System