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bytes.
Disk Storage Segments. (STORAGESEGDISK) Expect the size of the disk storage segment
metadata table to be quite volatile. As files are added to HPSS, disk storage segments will be created,
and as files are migrated to tape and purged from disk, they will be deleted. A rough estimate of the
number of disk storage segments can be obtained by estimating the number of files that will be
resident on disk in the subsystem for each Storage Class, then multiplying by the Average Number of
Segments parameter of the Storage Class.
Tape Storage Segments. (STORAGESEGTAPE) The tape storage segment metadata table grows as
the number of files stored in the subsystem increases. Storage segments are created to describe
contiguous chunks of data written on tapes. Segment sizes may vary greatly. The number of storage
segments found on a given tape is not limited by the Core Server. This number is a function of the
length of the files written on the tape, the VV block size, the size of the data buffer used to write the
tape, and other factors.
HPSS support representatives will help sites use this spreadsheet as they size the metadata disk
resources and allocate those resources for the various DB2 tablespaces.
3.5.4.4. DB2 Disk Space
This section explains the local file system disk space requirements to support DB2, other than for
database tables.
The disk space that DB2 requires falls into the following categories:
DB2 log
The DB2 log requires a filesystem in which transaction log files are stored. The number of
log files and size of the files is controlled by several database configuration parameters.
LOGFILSIZ determines the size of each log file and LOGPRIMARY + LOGSECOND
determine the total number of log files that could exist in the logging filesystem that you specify with
NEWLOGPATH. Each database should log to its own filesystem and must utilize a RAID device for
storing the data. Also, it is required to use the DB2 MIRRORLOGPATH configuration variable and
define a separate filesystem to store the mirrored log file.
When DB2 is first started, log files are placed in the /var/hpss/<instance_name>/NODE0000/...
directory. After DB2 is started, use the database configuration parameters NEWLOGPATH and
MIRRORLOGPATH to direct log files to a prepared location.
To determine the amount of disk space required for the DB2 log files, run:
% db2 get db cfg for <db name>
Look for the LOGFILSIZ variable, which is the size of each log file, and multiply it by the total
number of logs for this database (LOGPRIMARY + LOGSECOND). The result will be the number
of 4KB blocks needed. To convert this to the number of bytes, multiply the result by 4096. Calculate
this for each database that utilizes this particular log filesystem to determine the total necessary disk
space.
The optimal type of disk used for the log filesystem(s) is a low-latency disk since the I/O is
performed in many small chunks. To ensure full recoverability in the event of media failure on the
log disk, it is important to mirror the log on a separate physical disk.
DB2 database home directories
DB2 requires approximately 700MB of disk space for installation. Upon installation each database
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 77