blkio command

The blkio BASIC program displays or sets the I/O blocking factor, or number of frames read in one disk access during sequential file accesses. The setting is global for the whole system, and can be changed at any time.

For Windows: Not Supported


blkio {[factor|off]} {(options}


factor Turns the blocking factor off and on.
options q Quiet option does not display anything while setting the blocking factor.

The blkio command controls how many frames are read in one disk access by processes doing sequential file accesses, such as save or AQL processors. Without any argument, the current setting displays. If the mechanism is active, this message displays:

IO blocking factor set to n frames.

This indicates that sequential access reads n frames at each disk access. If the mechanism is disabled, this message displays:

IO blocking disabled.

This indicates that the I/O blocking mechanism is not active, and that frames are read one at a time.

The argument factor is the number of frames to be read at each disk access. The value of 1 or off disables the grouping of reads. The maximum number of frames that can be read is 64. For a complete description of the I/O blocking mechanism.

The blocking factor can also be set by adding this statement in the virtual machine configuration file:

blkio n

where n is the blocking factor.

The TCL buffers command allows monitoring the effect of blocking I/O, by the frame-faults counter.


Displays the current setting.

IO blocking factor set to 2 frames.

Sets the blocking factor to four frames, and suppresses the message.

blkio 4 (q

Disables the mechanism.

blkio off
IO blocking disabled.