Monitoring cache statistics

Cache statistics for each target device can be displayed by using the cache_mgt monitor get command.

For example, if hdisk1 is the only target device that is cached, the output of the cache_mgt command might be similar to the following example:

# cache_mgt monitor get -h -s
ETS Device I/O Statistics -- hdisk1
Start time of Statistics -- Mon Mar 27 07:10:41 2017
-----------------------------------------------------
 Read Count:                              152125803
 Write Count:                              79353626
 Read Hit Count:                                871
 Partial Read Hit Count:                         63
 Read Bytes Xfer:                    10963365477376
 Write Bytes Xfer:                    4506245999616
 Read Hit Bytes Xfer:                      48398336
 Partial Read Hit Bytes Xfer:               5768192
 Promote Read Count:                     2033078104
 Promote Read Bytes Xfer:           532959226494976

The cache_mgt command provides the following caching metrics:

Read Count: The total number of all the read operations that are issued by all applications to the target device. This value also includes the read operations to the cache device, if the data is available in the cache device. This value is the total number of separate read requests and does not indicate the size (byte count) of the read requests.
Write Count: The total number of write operations that are issued to the target device. This value is the total number of separate write requests and does not indicate the size (byte count) of the write requests.
Read Hit Count: The total number of read operations that were issued to the target device that are full read hits. A full read hit is a read operation instance in which a read request is fulfilled completely by the cache device. The Read Hit Count value is the total number of separate read hit requests and does not indicate the size (byte count) of the read requests. This value is included in the Read Count value.
Partial Read Hit Count: The total number of read operations that were issued to the target device that are partial read hits. A partial read hit is a read operation instance in which a read request is fulfilled partially by the cache device. The remaining data, which is not available in the cache device, must be acquired from the target device. The Partial Read Hit Count value is the total count of separate read requests and does not indicate the size (byte count) of the read requests. This value is included in the Read Count value.
Read Bytes Xfer: The total number of bytes that are transferred in all read requests that were issued from applications to the target device. This value represents the total byte count of full read hit data, partial read hit data, and any data that is acquired from the target device.
Write Bytes Xfer: The total number of bytes that are transferred in all write requests that were issued from applications to the target device.
Read Hit Bytes Xfer: The total number of bytes that are read during full read hit instances.
Partial Read Hit Bytes Xfer: The total number of bytes that are read during partial read hit instances.
Promote Read Count: The total number of read commands that are issued to the target device when the data is populated into the cache device. This value does not indicate the number of instances when the data is populated into the cache device because a single request to populate data into the cache device might be divided into multiple read operations if the maximum transfer size of data to the target disk is less than the request size.
Promote Read Bytes Xfer: The total number of bytes that are read from the target device when data is populated to the cache device.