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Source: VCA_VS file at the DETAIL timespan
Function: This facility helps to identify departments or
groups that are wasting DASD storage space due to
poor VSAM allocation practices. These problems
can be caused either by allocating more space than
is necessary, or by using other VSAM options
incorrectly. The Storage Administrator can
perform up to four different types of space
analysis with this facility, and can report the
results on one combined report or on separate
reports. Correction of the problems detected by
this facility may recover a large amount of
storage space with a small amount of effort.
The term "wasted space" in these reports refers to
any space that is allocated (so that it cannot be
used by others), and yet is not currently being
used to contain data. In some cases, such as the
overallocation of a data set to accommodate future
growth, this is normal. These reports also focus
strictly on wasted space, and do not consider
other factors such as performance. Before making
any changes to the VSAM data sets appearing on the
reports from this facility, it is strongly
suggested that other performance and application
factors be considered.
Features: Summary reports should be run regularly to monitor
wasted space, with more detailed reporting
occurring when problems are detected. A wide
variety of filtering and reporting options allow
many views of the same data to be obtained.
Summary reports can be produced as tabular
reports, printer graphics reports or color
graphics reports, and can be summarized based on
the data set name, the CA MICS accounting codes,
or using a Data Set Group table. Detail reports
may then be generated to isolate problems to the
data set level. If the detail report still does
not provide enough information, up to four
different analysis reports can be run.
SMS
Issues: Users planning for SMS could identify those groups
with the worst space usage values, as they may be
the best candidates for the immediate benefits of
SMS. As groups migrate to SMS control, regular
use of this report would verify that the expected
space savings from SMS are being realized.
COLUMN DESCRIPTIONS
Report Types
There are four different types of analysis
reports, corresponding with the four types of
wasted space checking done by this facility.
Generation of the four types of analysis reports
may be done in any combination, using options on
the report options screen. It is also possible to
have analysis done without an analysis report
being produced. The four types of analysis
reports are as follows:
RECORD/CI ANALYSIS
When defining a VSAM data set, the user
specifies, or allows to default, both the
record length and the control interval size.
If the record size does not fit evenly into
the control interval, some space will be
wasted within each control interval. This
wasted space may be reclaimed by selecting
better values for these parameters.
IMBED ANALYSIS
While use of the IMBED VSAM option is often
done for performance reasons, it wastes space
by reserving one track from every control area
for the embedded keys. This space could be
reclaimed by using a larger control area,
although that may be difficult as the user has
no direct control over this. A better
approach may be to examine those large data
sets that use embedded keys to see if an
alternate method would be possible.
BLOCK/TRACK ANALYSIS
Based on allocation parameters, VSAM
calculates the size of the physical block that
will be written for the data set. Space may
be wasted if a block size is selected that
does not fit well on the device being used.
In general, the larger the block size, the
more efficient the use of the track. Some of
this space may be reclaimed by specifying
larger values for some options, such as
control interval size, that will cause VSAM to
use a larger physical block size.
OVERALLOCATION ANALYSIS
As with an data set, it is possible to allocate a
VSAM data set with more space than is needed to
hold the data. Some overallocation is not bad, as
this gives the data set room to grow as more data
is added. But data sets with much overallocation
should be investigated, especially if they are
large. Some of this space may be reclaimed by
reallocation the data set with requesting a
smaller amount of storage space.
While the example shows only one of the four types
of analysis reports, all four types will be
described here. As the left side of each report
is similar, it will be described in a common
section. The unique columns on each of the four
types of reports will then be described.
COMMON DATA COLUMNS
The following data columns appear on the left side
of each report, and are common to each of the four
analysis reports:
Data Set Name
Indicates the name of the VSAM data set
represented by the statistics on this line of the
report. For VSAM clusters, this line may identify
the individual cluster component (such as Data or
Index), rather than the cluster name.
Data Set Size in MB
Represents the total amount of space being
allocated by this data set, expressed in
megabytes.
TOTAL Waste in MB
Represents the total amount of space currently
being wasted this data set. This value may
represent up to four different types of wasted
space.
% Alloc Space Waste
The percentage of the space allocated by this data
sets that is being wasted. This is calculated
using the two previous columns.
RECORD/CI ANALYSIS
The following data columns are unique to the Record/CI
Analysis report. They appear on the right side of the
report, after the common columns:
Record/CI Waste in MB
Represents the wasted space in this data set
caused by record sizes that are not efficient for
the control interval size being used. This value
is expressed in megabytes.
Control Interval Size
Lists the control interval size for this data set,
expressed in bytes.
Better CI Size
If possible, the report will attempt to calculate
a better control interval size than the one being
used. If this column is not blank, you may wish
to try the suggested value. The report only
attempts to calculate this using the most common
control interval sizes (512K, 1024K, 2048K, 4096K
and 8192K), so you be able to calculate your own
better value based on the requirements of the
application that uses the data.
Record Size
Indicates the logical record length (LRECL)
specified when the data set was created.
% of each CI Wasted
Indicates the percentage of each control interval
that is wasted, due to the size of the records
being used.
IMBED ANALYSIS
The following data columns are unique to the Imbed
Analysis report. They appear on the right side of the
report, after the common columns:
Imbed Waste in MB
Represents the wasted space in this data set
caused by the use of the IMBED attribute. This
value is expressed in megabytes.
Data Set Format
Indicates the VSAM data set format for this data
set.
Control Area Size in Bytes
Indicates the VSAM control area size, expressed in
bytes.
Control Area Size in Tracks
Indicates the VSAM control area size, expressed in
tracks.
% of each CA Wasted
Indicates the percentage of each control area that
is being used for embedded keys and cannot be used
for other data storage.
BLOCK/TRACK ANALYSIS
The following data columns are unique to the Block/Track
Analysis report. They appear on the right side of the
report, after the common columns:
Block/Trk Waste in MB
Represents the wasted space in this data set
caused by the size of the physical blocks
being written on each track. This value is
expressed in megabytes.
Device Type
Indicates the type of device on which this data
set is stored.
Device Track Size
Indicates the maximum amount of data that may be
stored on one track for this type of device.
Block Size
Indicates the physical block size used by VSAM for
storing the records within this data set.
Blocks Per Track
Indicates the number of blocks that are written on
each track for this data set.
% of each Trk Wasted
The percentage of each track that cannot be used
for data storage, due to the physical block size
and the gaps that exist between physical blocks.
In general, the smaller the block size, the more
waste that will occur.
OVERALLOCATION ANALYSIS
The following data columns are unique to the
Overallocation Analysis report. They appear on the
right side of the report, after the common columns:
OverAlloc Waste in MB
Represents the wasted space in this data set
caused by allocating more space than is necessary
to contain the data. This value is expressed in
megabytes.
Data Set Format
Indicates the VSAM data set format for this data
set.
Allocated Space in Tracks
Indicates the total amount of space allocated for
this data set, expressed in DASD tracks.
Used Space in Tracks
Indicates the amount of space allocated to this
data set that is actually being used for the
storage of data, also expressed in DASD tracks.
Percent Space Unused
Indicates the percentage of the allocated space
that is not being used for data storage. This
value is calculated from the previous two columns.
VSAM WASTED SPACE (STGECF) CA MICS StorageMate - RECORD/CI ANALYSIS ABC CORPORATION ------------------------------------------------------------ SYSID=IMS8 ------------------------------------------------------------ Data Set Name Data Set TOTAL % Alloc | Record/CI Control Better Record % of Size in Waste Space | Waste Interval CI Size each CI MB in MB Wasted | in MB Size Size Wasted INFOTEST.VSAM.DATA 332 103 31 | 31 4096 8192 600 12 COS.PROD.DB5.SDDS.DATA 1309 284 22 | 26 8192 2000 2 COS.PROD.DB2.SDDS.DATA 877 183 21 | 18 8192 4000 2 INFOTST.ONE.VSAM.DATA 120 30 25 | 12 4096 8192 600 12 SYS5.AAA.STAINST.SDDS.DATA 68 19 28 | 8 8192 3500 15 SLSTST.CD1TRB.DATA 672 148 22 | 6 24576 4856 1 COS.PROD.DB0.SDDS.DATA 409 130 32 | 6 8192 669 2 DSICTST.DDIRD 94 18 19 | 5 4096 8192 384 6 SYS9.FIN.ONLI.DATA 142 36 25 | 5 22528 1800 4 TESTFIN.AMX101B.DATA 107 19 17 | 4 8192 600 5 TESTFIN.AMX100A.DATA 107 19 17 | 4 8192 600 5 PRODDEV.TESTING.MCF.STAGE2.DATA 127 61 48 | 4 8192 640 6 COS.TEST.CONVERT.SDDS.DATA 238 85 36 | 4 8192 2000 2 TESTFIN.AMX101A.DATA 85 15 17 | 4 8192 600 5 BTEST.RUN40.DXVBNHG0.DATA 98 22 22 | 3 32768 2250 4 -------------------------------------------- -------- -------- -------- SYSID 4786 1171 141 ======== ======== ======== 4786 1171 141 N= 15
Figure 4-86. VSAM Wasted Space / Analysis
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