# Cache Control Unit

The Cache Control Unit attributes provide performance and status information for cache control units.

Active Volumes: The number of volumes with ACTIVE caching status on the cache control unit.

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 or promoted to cache. Also, the entries of tracks in the LRU list are not updated.

Cache MB Available: The total, in megabytes, of cache storage available on this Cache Control Unit.

Cache MB Configured: The total storage, in megabytes, of cache storage configured on this Cache Control Unit.

Cache Status: The caching status for this subsystem. Values are as follows: Active (in other words, caching for this subsystem is active), Inactive (in other words, caching for this subsystem is inactive), Pending Active, Pending Inactive, and Timeout.

CFW Read Percent: The percentage of all I/Os that were Read operations for data in cache that originated from a cache fast write during this interval. Cache fast write (CFW) is a form of fast write where the data is written directly to cache without using nonvolatile storage and is available for later destaging.

CFW Write Percent: The percentage or all I/Os that were Cache Fast Writes during this interval. Cache fast write (CFW) is a form of fast write where the data is written directly to cache without using nonvolatile storage and is available for later destaging.

Control Unit Type: The type of this cache control unit. This field is only populated for the physical devices that are supported with extended information. Examples of these devices include EMC Symmetrix, 2105, and 2107.

Deactivated Volumes: The number of volumes on this Cache Control for which the cache has been deactivated.

DFW Hit Percent: The percentage of all DASD I/Os to this control unit that were DASD Fast Writes during this interval. DASD Fast Write (DFW) is form of fast write to cache where the data is written concurrently to cache and nonvolatile storage and automatically scheduled for destaging to DASD.

DFW Retry Percent: The percentage of DASD I/O operations which required retry during this interval.

Inhibit Cache Percent: The percentage of I/O operations which inhibited the loading of data into cache.

Managed System: The SMS name of this system.

NVS KB Configured: The kilobytes of cache storage configured on this subsystem. NVS (nonvolatile storage) facilitates the DASD Fast Write feature which allows data to be written at electronic speeds directly into this nonvolatile memory in the controller, thus avoiding the many delays associated with accessing the actual disk.

NVS KB Pinned: The amount of storage that is unavailable because DASD failure is preventing the subsystem from destaging data. The data is pinned in cache.

NVS Status: The overall status of the nonvolatile storage (NVS). Values are:

- Active=1 NVS is online and usable.
- Inactive=2 NVS is not usable.
- Pending_Active=3 Status is switching from inactive to active.
- Pending_Inactive=4 Status is switching from active to inactive.
- Timeout=0 Status is timed out.

Read Hit Percent: The percentage of read hits for each cache control unit.

Read I/O Percent: The percentage of I/O requests to the cache control unit that were read requests.

Serial Number Index: The serial number of the control unit. Used as an index into hardware specific displays.

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

Storage Facility Series: The series of control unit, which defines the physical geometry of the subsystem. Can be one of: HDS, Symmetrix, Iceberg, RAMAC®, shark, DS6000™, or DS8000™.

Subsystem ID Fullword: The subsystem ID (for Model 3990, 2105, and 2107 control units).

Subsystem ID Hex: The subsystem ID (for Model 3990, 2105, and 2107 control units).

Subsystem ID: The subsystem ID (for Model 3990, 2105, and 2107 control units).

Time Stamp: The date and time this data was reported. Primarily for use in historical reporting.

Track Destaging Rate: The number of tracks per second being removed from cache to physical disks over the cache interval.

Track Staging Rate: The number of tracks per second being brought into cache from the physical disks over the cache interval.

Write Hit Percent: The percentage of I/O operations that completed without accessing the hard disk drive.