Measure Reference Manual

ENDING-FREE-SPACE
Number of bytes free on the volume at the time indicated by the TO time. This counter is updated
only for the primary path record. The RATE attribute has no effect on how this counter is displayed.
The primary path can be obtained from the LIST DISC command (Measure H03 and later PVUs)
or the SCF INFO DISCNAME, DETAIL command.
Counter type: Snapshot.
FREE-SPACE-IOS
Number of I/O operations to the disk free space table.
The disk free space table lists each available free block on the disk. The disk process modifies the
table when file extents are allocated or deallocated. Choosing the proper extent sizes and avoiding
unnecessary file creations and deletions can help reduce the number of free space I/Os.
Counter type: Incrementing.
INPUT-BYTES
Number of bytes read from the disk. In addition to programmatic read operations, write operations
and various commands (for example, LISTHEADERS and LISTDEFECTS) also cause bytes to be read
from the disk.
The disk process reads one or more blocks of data during a read operation, depending on the
structure of the file and amount of data being read:
• For unstructured files, the disk process reads at least one block of data. If a record crosses
block boundaries, the disk process must read two blocks of data. Also, if you are writing a
partially filled block to disk, the disk process must read the block, merge the new data into
the block, and then write the block to disk.
• For structured files, the disk process reads a block of data as specified by the file block size.
• For key-sequenced files, to read a data block, the disk process might have to read one or
more index blocks as well.
Because the I/O process modifies this counter before an I/O operation, if the read fails, the byte
count might not be accurate.
In D-series and G-series RVUs, this is a 32-bit counter. In H-series and J-series RVUs, this is a 64-bit
counter.
In G-series RVUs, the INPUT-BYTES-F field is a 64-bit version of INPUT-BYTES.
Counter type: Accumulating.
OUTPUT-BYTES
Number of bytes written to the disk. In addition to programmatic write operations, many commands
(for example, FORMAT and LOADMICROCODE) also write to the disk.
The disk process writes one or more blocks of data on a write operation, depending on the structure
of the file and amount of data being written:
• For unstructured files, the disk process writes at least one block of data. If a record crosses
block boundaries, the disk process must write two blocks of data. In addition, if you are writing
a partially filled block to disk, the disk process must read the block (counted by INPUT-BYTES),
merge the new data into the block, and then write the block to disk.
• For structured files, the disk process writes a block of data as specified by the file block size.
• For key-sequenced files, the disk process writes to the data block and might also have to
update the index block.
Buffered writes can save I/Os because the disk process collects the updates and writes them out
only when necessary.
DISC 199