Cache subsystem status and overview
The first section shows the configuration of the selected storage subsystem. This includes the
amount of cache configured (installed) and available for use, and how much storage, if any, is
pinned because of a DASD failure.
Finally, the overall subsystem status shows whether
NON-VOLATILE STORAGE and CACHE FAST WRITE are active.
The second section provides details of the cache usage of the subsystem. Here, the analyst can see at a glance all the I/O requests to the subsystem, divided into the categories NORMAL, SEQUENTIAL, and CACHE FAST WRITE. READ and WRITE requests are shown separately as totals, rates, or ratios.
Note: All values shown as RATE are calculated on the basis of seconds that are shown in the CINT
value in the report header.
C A C H E S U B S Y S T E M A C T I V I T Y
PAGE 1
z/OS V2R4 SYSTEM ID SYS1 DATE 05/11/2019 INTERVAL 10.00.010
RPT VERSION V2R4 RMF TIME 08.50.00
SUBSYSTEM 2107-01 CU-ID B005 SSID 1800 CDATE 05/11/2019 CTIME 08.50.00 CINT 10.00
TYPE-MODEL 2107-981 MANUF IBM PLANT 75 SERIAL 0000000YT111
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CACHE SUBSYSTEM STATUS
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SUBSYSTEM STORAGE NON-VOLATILE STORAGE STATUS
CONFIGURED 252128M CONFIGURED 16384M NON-VOLATILE STORAGE - ACTIVE
AVAILABLE 216498M PINNED 0.0 CACHE FAST WRITE - ACTIVE
PINNED 0.0
OFFLINE 0.0
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CACHE SUBSYSTEM OVERVIEW
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TOTAL I/O 85821 CACHE I/O 85821
TOTAL H/R 1.000 CACHE H/R 1.000
CACHE I/O -------------READ I/O REQUESTS------------- ----------------------WRITE I/O REQUESTS---------------------- %
REQUESTS COUNT RATE HITS RATE H/R COUNT RATE FAST RATE HITS RATE H/R READ
NORMAL 35724 59.5 35724 59.5 1.000 15454 25.8 15454 25.8 15454 25.8 1.000 69.8
SEQUENTIAL 23279 38.8 23279 38.8 1.000 11364 18.9 11364 18.9 11364 18.9 1.000 67.2
CFW DATA 0 0.0 0 0.0 N/A 0 0.0 0 0.0 0 0.0 N/A N/A
TOTAL 59003 98.3 59003 98.3 1.000 26818 44.7 26818 44.7 26818 44.7 1.000 68.8
-----------------------CACHE MISSES----------------------- ----------------MISC---------------
REQUESTS READ RATE WRITE RATE TRACKS RATE COUNT RATE
DELAYED DUE TO NVS 0 0.0
NORMAL 0 0.0 0 0.0 0 0.0 DELAYED DUE TO CACHE 0 0.0
SEQUENTIAL 0 0.0 0 0.0 0 0.0 DFW INHIBIT 0 0.0
CFW DATA 0 0.0 0 0.0 ASYNC (TRKS) 14737 24.6
TOTAL 0 RATE 0.0
---CKD STATISTICS--- ---RECORD CACHING-- --SYNCH I/O ACTIVITY-- -HOST ADAPTER ACTIVITY- --------DISK ACTIVITY-------
REQ HITS BYTES BYTES RESP BYTES BYTES
WRITE 0 READ MISSES 0 /SEC /REQ /REQ /SEC TIME /REQ /SEC
WRITE HITS 0 WRITE PROM 17037 READ 7.0 1.000 READ 3.7K 362.4K READ 0.000 0 0
WRITE 0.0 0.000 WRITE 3.7K 163.8K WRITE 17.124 16.0K 344.1K| Field Heading | Meaning |
|---|---|
| SUBSYSTEM | Storage subsystem type (as configured). |
| CU-ID | Physical control unit number of the caching subsystem. This is equal the lowest device number, or to the device that has been turned online first, respectively. |
| SSID | Subsystem identifier: a number assigned during installation of the subsystem that uniquely identifies the storage subsystem. |
|
Note: Device reserve activity can cause a data gatherer interface to wait until a reserve has been
released. This in turn can cause the cache interval to be much longer than a regular RMF
interval.
Therefore, CDATE, CTIME and CINT have been introduced to show the actual point in time to which the cache interval start is related, and the actual cache interval length. All rates shown in the report are based on CINT, not on INTERVAL. |
|
| CDATE | Date when the cache interval started. |
| CTIME | Time when the cache interval started. |
| CINT | Cache interval time. In interval reports, the format is mm.ss, while in duration reports the format is hh.mm.ss. |
| TYPE-MODEL | Device type and model. |
| TYPE MODEL MANUF PLANT SERIAL | The hardware description of the disk system. |
| VOLSER | Volume serial number of the reported DASD device (only for device-level reporting). |
| NUM | Device number of the reported DASD device (only for device-level reporting). |
| Field Heading | Meaning |
|---|---|
|
Note: The reported storage capacities for cache and non-volatile storage (NVS) represents only the
Cluster Processor Complex in the storage server, that controls the subsystem. Since a typical
storage server has two clusters, you must double the reported capacities to get the actual
sizes.
|
|
| SUBSYSTEM STORAGE | Physical capacity of random access cache (in megabytes). |
| CONFIGURED | Amount of storage that is installed in this storage subsystem. |
| AVAILABLE | Amount of storage that is available for caching. This is the total cache size minus the amount used by the subsystem for the cache directory, minus the amount pinned and offline storage. |
| PINNED | Amount of storage that is unavailable because a DASD failure is preventing the subsystem from destaging the data. The data is pinned in cache. |
| OFFLINE | Amount of storage that is offline because of a host or subsystem error. |
| NON-VOLATILE STORAGE (NVS) | Physical capacity of random access storage with a backup battery power source (in megabytes). |
| CONFIGURED | Amount of NVS that is installed in this storage subsystem. |
| PINNED | Amount of NVS that is unavailable because a DASD failure is preventing the subsystem from destaging the data. The data is pinned in NVS. |
| STATUS | The caching status of the entire subsystem. |
| NON-VOLATILE STORAGE | Overall status of the non-volatile storage (NVS).
|
| CACHE FAST WRITE | Status of the CACHE FAST WRITE (CFW) option.
Note: CFW does not use NVS.
|
| Field Heading | Meaning |
|---|---|
| TOTAL I/O | Total number of I/O requests to cached devices in the storage subsystem. |
| TOTAL H/R | Ratio of I/Os that were processed within the cache (cache hits) based on the total number of I/Os. |
| CACHE I/O | Total number of cacheable I/O requests to cached devices in the storage subsystem. This value excludes INHIBIT CACHE LOAD and CACHE BYPASS I/O requests. |
| CACHE H/R | Ratio of I/Os that were processed within the cache (cache hits) based on the total number of cacheable I/O requests. |
| CACHE I/O REQUEST - The channel command DEFINE EXTENT specifies the way the cache will be used. There are three categories (NORMAL, SEQUENTIAL, CFW DATA) and a TOTAL value: | |
| NORMAL | Cache will be managed by least-recently-used (LRU) algorithm for making cache space available. |
| SEQUENTIAL | Tracks following the track assigned in the current CCW chain are promoted. They will be transferred from DASD to cache in anticipation of a short-term requirement. |
| CFW DATA | WRITE and READ-AFTER-WRITE requests are processed in cache. The data might not be written to DASD. Because CFW does not use the NVS, the application is responsible for restoring the data after a cache or subsystem failure. |
| TOTAL | This is either the sum of I/O requests, the total I/O rate, or the average hit ratio for the three categories previously described. |
| READ I/O REQUESTS - Cache I/O requests that searched or read data from DASD. This is the number of channel operations that had at least one SEARCH or READ command but no WRITE commands. This is counted for cached devices only. | |
| COUNT | Total number of SEARCH/READ requests. |
| HITS | Number of SEARCH/READ requests that completed without accessing the DASD. |
| H/R | Hit Ratio - number of SEARCH/READ hits compared to the total number of SEARCH/READ requests. |
| WRITE I/O REQUESTS - Cache I/O requests that wrote data to DASD. This is the number of channel commands that had at least one WRITE command. It is counted for cached devices only. | |
| COUNT | Total number of WRITE requests. |
| FAST | Total number of DASD/CACHE FAST WRITE requests. |
| HITS | Number of DASD/CACHE FAST WRITE requests that completed without accessing the DASD (fast write hit). |
| H/R | Number of DASD/CACHE FAST WRITE hits compared to the sum of all READ and WRITE requests (excluding ICL and BYPASS). |
| %READ | Percentage of READ requests compared to the sum of all READ and WRITE requests (excluding ICL and BYPASS). |
| CACHE MISSES -Cache misses are calculated as the difference
between total I/O requests and the number of cache hits. They are shown for normal, sequential, and
CFW requests. A cache miss occurs if a record that is to be read from or written to a data set is not found in the cache. In either case, the track in which this record is located is searched on the DASD and transferred to cache. Subsequent requests referring to the same record can then be processed in cache only, provided that the data has not yet been moved out because cache space is needed for other data. Other reasons for cache misses are DFW bypass and DFW inhibit. In the first case, a lack of NVS caused the data to be written to DASD immediately, while in the second case, usage of DFW is inhibited (for example, the device does not allow DFW). |
|
| READ | Number of SEARCH/READ requests that needed access to DASD because the data could not be found in the cache. |
| WRITE | Number of WRITE requests that needed access to DASD because the data could not be found in the cache. |
| TRACKS | Number of tracks transferred from DASD to cache. |
| TOTAL | Total number of I/O requests that needed access to DASD because the data could not be found in the cache. |
| MISC - Miscellaneous cache activities | |
| DELAYED DUE TO NVS |
DASD Fast Write operations delayed due to non-volatile storage space constraints. |
| DELAYED DUE TO CACHE |
Operations delayed due to cache space constraints. |
| DFW INHIBIT | If DASD FAST WRITE is active, this is the number of WRITE requests that inhibited DASD FAST WRITE. If DASD FAST WRITE is inactive, this is the number of WRITE requests that directly accessed the DASD, even with DASD FAST WRITE turned on. |
| ASYNC | Number of tracks transferred from cache to DASD asynchronously to transfer from the channel
to release space in the cache and the NVS. A high number of ASYNC I/Os is an indicator for an over-committed cache or NVS. |
| CKD STATISTICS - CKD (Count-Key-Data) is a format used to store data on DASD. The counts shown in this section are contained in the total write count. | |
| WRITES | Number of write I/O requests in CKD format. |
| WRITE HITS | Number of write I/O requests in CKD format that could be resolved in the cache. |
| RECORD CACHING - Record caching is done dynamically upon a decision made by DCME or the microcode. It may improve overall cache performance if caching of whole tracks would waste cache storage. The decision is based on the number of I/Os, the hit ratio, and the locality of reference of a certain entity of data. | |
| READ MISSES | Number of instances in which a record requested for READ was not found in the cache, and access to DASD was required. |
| WRITE PROM | Number of instances in which a record requested for WRITE was found in the cache, and access to DASD was not required. |
| SYNCH I/O ACTIVITY - Synchronous I/O read and write activities | |
| REQ/SEC | The average number of synchronous I/O read and write requests per second. |
| HITS/REQ | Ratio of cache hits for synchronous I/O read and write requests. |
| HOST ADAPTER ACTIVITY1) - I/O activity of normal, sequential and CFW read and write requests. | |
| BYTES/REQ | The average number of transferred bytes per read and write request. |
| BYTES/SEC | The average number of transferred bytes per second for read and write requests. |
| DISK ACTIVITY1) - Transfer activity from hard disk to cache and vice versa. | |
| RESP TIME | Response time in milliseconds per read and write request. |
| BYTES/REQ | The average number of transferred bytes per read and write request. |
| BYTES/SEC | The average number of transferred bytes per second for read and write requests. |
| 1) available for the IBM TotalStorage DS family | |
Duration reports: An asterisk behind a status field or the field VOLUME SERIAL indicates that the contents of the field has changed during the duration interval.