# Cache Devices

The Cache Devices attributes provide both cache status and cache performance information for a logical volume.

Avg Logical KB Read: The average number of kilobytes read from the logical volume per second over the cache interval.

Avg Logical KB Written: The average number of kilobytes written to the logical volume per second over the cache interval.

Avg Logical Read Time: The average time in milliseconds spent reading from the logical volume per I/O over the cache interval.

Avg Logical Write Time: The average time in milliseconds spent writing to the logical volume per I/O over the cache interval.

Avg Phys Read Response Time: The average time to read from the physical disk per operation in milliseconds over the cache interval.

Avg Phys Write Response Time: The average time in milliseconds to write to the physical disk per operation over the cache interval.

Bypass Cache Percent: The percentage of I/Os that bypassed cache during this interval. The I/O request is sent directly to DASD. Tracks are not read from cache and are not promoted to cache, and their entries in the LRU list are not updated.

Cache Status: The caching status for the subsystem to which this device is attached. Active means caching for this subsystem is active. Inactive means caching for this subsystem is disabled.

Cache to DASD Total Tracks: The number of tracks written from cache to physical disk during the cache interval. This value is captured asynchronously with respect to the transfer of data from the channel to the cache.

Cache to DASD Tracks per Second: The rate per second of tracks written from cache to physical disk during the cache interval. This value is captured asynchronously with respect to the transfer of data from the channel to the cache.

CFW Read Percent: The percentage of READ requests which were satisfied from cache due to a previous cache fast write.

CFW Write Percent: The percentage of all I/Os that were CACHE FAST WRITES during this interval. CACHE FAST WRITE allows data to be written to cache only. The data is later written to DASD. CFW differs from DASD Fast Write in that the data is not written to nonvolatile storage (NVS).

Channel Index: The identifier for channel path that identifies which channel path this device is attached to.

Control Unit Model: The model number of the control unit to which this device is attached.

DASD to Cache Non-promotes per Second: The rate per second of operations that did not promote (copy) a track to cache because free cache segments were not available.

DASD to Cache Non-promotes: The number of operations that did not promote (copy) a track to cache because free cache segments were not available.

DASD to Cache Total Tracks Non-sequential: The number of tracks read from physical disk to cache over the cache interval for non-sequential I/O operations.

DASD to Cache Total Tracks Sequential: The number of tracks read from physical disk to cache over the cache interval for sequential I/O operations.

DASD to Cache Total Tracks: The number of tracks read from physical disk to cache over the cache interval for I/O operations.

DASD to Cache Tracks per Sec: The rate per second of tracks read from physical disk to cache over the cache interval for I/O operations.

DASD to Cache Tracks per Second Non-sequential: The rate per second of tracks read from physical disk to cache over the cache interval for non-sequential I/O operations.

DASD to Cache Tracks per Second Sequential: The rate per second of tracks read from physical disk to cache over the cache interval for sequential I/O operations.

Device Address: The four hexadecimal digits that define the physical address of this device. Also known as unit or unit address.

Device Hex Address: The four-digit hexadecimal address of this device.

DFW Hit Percentage: The percentage of DASD Fast Writes that were satisfied from cache without requiring access to DASD. DASD Fast Writes are written to both cache and nonvolatile storage (NVS).

DFW Retry Percentage: The percentage of DASD Fast Write operations that did not complete due to nonvolatile Storage (NVS) constraints.

DFW Status: The status of DASD FAST WRITE function for this volume. Values are Active, Inactive, Unknown, or Timeout.

Extent Pool ID: The Extent Pool Identifier.

I/O Count: The number of cache eligible I/Os to the device over the cache collection interval.

Inhibit Cache Percentage: The percentage of I/O requests that set the Inhibit Cache Load mode in the channel program to prevent the data being cached. If the data is already in cache, the request is satisfied from cache.

Logical Control Unit Index: The number of LCU to which this device is attached. An LCU is the logical representation of either a single control unit, with or without attached devices, or a group of control units that share devices.

Logical KB Read: The total number of kilobytes read from the logical volume over the cache interval.

Logical KB Written Total: The total number of kilobytes written to the logical volume over the cache interval.

Logical Read Time: The amount of time in milliseconds spent reading from the logical volume over the cache interval.

Logical Write Time: The amount of time in milliseconds spent writing to the logical volume over the cache interval.

Managed System: The SMS name of this system.

Physical Device: The identifier of the physical device type of this device.

Physical KB Read Rate: The kilobytes read from the physical disk per second over the cache interval.

Physical KB Read Total: The total kilobytes read from the physical disk over the cache interval.

Physical KB Write Rate: The kilobytes written to the physical disk per second over the cache interval.

Physical KB Write Total: The total kilobytes written to the physical disk over the cache interval.

Physical Read Rate: The rate of I/O read operations from the physical disk per second over the cache interval.

Physical Read Total: The total number of I/O read operations from the physical disk over the cache interval.

Physical Write Rate: The rate of I/O write operations to the physical disk per second over the cache interval.

Physical Write Total: The total number of I/O write operations to the physical disk over the cache interval.

RAID Flag: Indicates the type of RAID device.

Read Hit Percent: The percentage of READ requests that were satisfied from cache.

Read I/O Count: The number of read requests for this device.

Read I/O Percent: The percentage of I/O requests that are read requests.

Solid State Device: Indicates whether the logical volume is backed by a solid state physical device.

SSID Index: The fullword representation of the SSID used for indexing the product.

Storage Facility ID: The storage facility identifier for the device (Type-Model-Serial Number).

Storage Group Index: The name of the storage group to which this volume belongs. The storage group is an SMS construct used to group DASD devices in order to separate the physical requirements of storing data from the logical requirements.

Subsystem ID Hex: The subsystem ID associated with this device.

Subsystem ID Selector: An index to limit the range of physical volumes for which data is requested.

Subsystem ID: The two-byte unique value used to identify a 3990 or equivalent storage control unit.

Time Stamp: Represents the date and time this data was collected.

Total Phys Read Response Time: The total time to read from the physical disk in milliseconds over the cache interval.

Total Phys Write Response Time: The total time to write to the physical disk in milliseconds over the cache interval.

User Group Index: A user DASD group is an OMEGAMON II® facility that enables you to define groups of DASD volumes by VOLSER and device address. You can also specify generic VOLSERs and devices (patterns) by using the wildcard character.

Volume: The volume serial number of the disk device.

Write Hit Percent: The percentage of I/O WRITE operations that were satisfied without having to access the physical drive. This occurs as the result of DASD Fast Write or Cache Fast Write features. DASD Fast Write is a default in controllers that support it. Cache Fast Write can be requested in the Define Extent command of the channel program.

Write I/O Count: The number of write requests for this device.