Mike Glass and Bob Rinne

NT Disk Performance Monitor - DiskPerf.Sys

The NT disk performance driver will be loaded and initialized after all other
disk device drivers in the system. It will then attach to all device objects
for partitions, including partition 0 (whole disk).

Taking advantage of the NT IO layered design, this single driver can be used
to monitor all disk activity in a system and will save the time of adding
device control support to all of the disk device drivers.

Disk performance will be measured for each logical volume (ie partition) and
cumulative counts will be kept for the whole disk.

The disk performance driver will support the following device controls:

typedef struct _DISK_PERFORMANCE {
        LARGE_INTEGER BytesRead;
        LARGE_INTEGER BytesWritten;
        LARGE_INTEGER ReadTime;
        LARGE_INTEGER WriteTime;
        ULONG ReadCount;
        ULONG WriteCount;
        ULONG QueueLength;
} DISK_PERFORMANCE, *PDISK_PERFORMANCE;

BytesRead, BytesWritten - Separate counters will be kept for I/O to each
        partition and to each drive. The drive is the cumulative for each
        partition on the drive plus the RAW accesses. Depending on whether
        the device control is called with the device object of partition 0
        or of a logical volume you will get the appropriate results. Note
        that calling the device control for partition 0 (whole disk) requires
        special security access (workstation manager, system).
        This counter will roll over on the 2**64 bit.

ReadTime, WriteTime - This is a count of the total time spent processing
        requests. The byte counts provide
        disk throughput. This measure is calculated by timestamping a request
        as it is received by the disk performance driver and timestamping it
        when it is completed. We could add minimum and maximum here if anyone
        was interested.

ReadCount, WriteCount - These counters keep track of the number of requests
        (IRPs) received.

Queue length - Jeff suggested that the way to keep track of this is to just
        count the outstanding requests to a partition or drive. We strongly
        agree.

As for free space within a partition, this is a measure that filesystems might
be able to provide. The disk device drivers have no concept of this.


The disk performance driver will use IoAttachDevice to insert itself in the
path of all drives in the system.