Performance metrics for volumes on SAN Volume Controller and Storwize systems

A storage environment can include SAN Volume Controller systems, Storwize® V7000 systems, and a Storwize V7000 Unified systems. You can include performance metrics for volumes, caches, and other data for volumes on these systems in performance reports.

Volume data

You can create performance reports that include the following information:

Overall Read I/O Rate (ops/s)

The average number of read operations per second. This value includes both sequential and nonsequential read operations.

Overall Write I/O Rate (ops/s)

The average number of write operations per second. This value includes both sequential and nonsequential write operations.

Total Overall I/O Rate (ops/s)

The average number of read operations and write operations per second. This value includes both sequential and nonsequential operations.

Maximum Read I/O Rate (ops/s)

The maximum read I/O rate of the volume in operations per second. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize™.

Maximum Write I/O Rate (ops/s)

The maximum write I/O rate of the volume in operations per second. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Maximum Write I/O Size (KiB)

The maximum size of write I/O operations in kibibytes. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Read Data Rate (MiB/s)

The average number of MiBs per second that are transferred for read operations.

Write Data Rate (MiB/s)

The average number of MiBs per second that are transferred for write operations.

Total Data Rate (MiB/s)

The average number of MiB per second that are transferred for read operations and write operations.

Read Response Time (ms/op)

The average number of milliseconds to complete a read operation.

Write Response Time (ms/op)

The average number of milliseconds to complete a write operation.

Maximum Read Response Time (ms/op)

The maximum read response time of the volume in milliseconds per operation. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Maximum Write Response Time (ms/op)

The maximum write response time of the volume in milliseconds per operation. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Overall Response Time (ms/op)

The average number of milliseconds to complete an I/O operation. This value includes both read and write operations.

Read Transfer Size (KiB/op)

The average number of KiB that are transferred per read operation.

Write Transfer Size (KiB/op)

The average number of KiB that are transferred per write operation.

Overall Transfer Size (KiB/op)

The average number of KiB that are transferred per I/O operation. This value includes both read and write operations.

Volume Utilization

The average percentage of time that the volume is busy.

Maximum Volume Utilization Percentage

The maximum period in percentage that the volume is busy. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Cache data

You can create performance reports that include the following information:

Write Cache Overflow I/O Rate (ops/s)

The average number of tracks per second that are written but are delayed because there is not enough space in the write cache. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Write Cache Delay I/O Rate (ops/s)

The average number of I/O operations per second that are delayed because of space constraints in the write cache, or because of other conditions.

This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3. The metric is an approximation because actual transfer rates are different for each cache layer. Therefore, you cannot directly compare this metric from resources that are 7.3 or later with earlier versions.

Write Cache Flush Through I/O Rate (ops/s)

The average number of tracks per second that are written to disk in flush-through mode. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Write Cache Write Through I/O Rate (ops/s)

The average number of tracks per second that are written to disk in write-through mode. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Maximum Write Cache Delay I/O Rate (ops/s)

The maximum number of delayed I/O operations per second for the volume, where the delay occurred because of space constraints or other conditions.

This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Overall Read Cache Hit Percentage

The percentage of all read operations that find data in the cache. This value includes both sequential and random read operations, and read operations in the volume cache and volume copy cache where applicable.

You can use this value to understand throughput or response times. Low cache-hit percentages can increase response times because in the event of a cache miss, the data must be read from the back-end storage resources.

Overall Write Cache Hit Percentage

The percentage of all write operations that are handled in the cache. This value includes both sequential and random write operations, and write operations in the volume cache and volume copy cache where applicable.

Total Overall Cache Hit Percentage

The percentage of all read operations and write operations that are handled in the cache. This value includes both sequential and random read and write operations, and read and write operations in the volume cache and volume copy cache where applicable.

You can use this value to understand throughput or response times. Low cache-hit percentages can increase response times because a cache miss requires access to the back-end storage resources.

Disk to Cache Transfer Rate (ops/s)

The average number of sectors or tracks per second that are transferred per second from the disks to the cache. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3. The metric is an approximation because actual transfer rates are different for each cache layer. Therefore, you cannot directly compare this metric from resources that are 7.3 or later with earlier versions.

Cache to Disk Transfer Rate (ops/s)

The average number of sectors or tracks per second that are transferred from the cache to the disks. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3. The metric is an approximation because actual transfer rates are different for each cache layer. Therefore, you cannot directly compare this metric from resources that are 7.3 or later with earlier versions.

Write Cache Delay Percentage

The percentage of I/O operations that are delayed because of space constraints in the write cache, or because of other conditions. The value is a percentage of all operations.

This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3. The metric is an approximation because actual transfer rates are different for each cache layer. Therefore, you cannot directly compare this metric from resources that are 7.3 or later with earlier versions.

Read Ahead Percentage of Cache Hits

The percentage of all read cache hits that occur on pre-staged data. This value applies only to the volume copy cache if the resource is running IBM Storage Virtualize 7.3 or later.

Dirty Write Percentage of Cache Hits

The percentage of all cache write hits that occur on data in the cache that is marked as modified. This value represents how effectively write operations are coalesced before the data is written to disk. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Write Cache Overflow Percentage

The percentage of write operations that are delayed because there is not enough space in the write cache.

Write Cache Flush Through Percentage

The percentage of tracks that are written to disk in flush-through mode. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Write Cache Write Through Percentage

The percentage of tracks that are written to disk in write-through mode. This value applies only to resources that are running a version of IBM Storage Virtualize earlier than 7.3.

Maximum Read Cache Hit Percentage

The maximum number of cache hits in percentage for sequential and nonsequential read operations for the volume over a specified interval. This metric is available only for hourly data and daily data for resources that are running IBM Storage Virtualize.

Other data

You can create performance reports that include the following information:

Global Mirror Write I/O Rate (op/s)

The average number of write operations per second that are issued to the Global Mirror secondary site.

Global Mirror Overlapping Write Percentage

The percentage of overlapping write operations that are issued by the Global Mirror primary site. Some overlapping writes are processed in parallel and are excluded from this value.

Applies to resources that are running IBM Storage Virtualize.

Global Mirror Overlapping Write I/O Rate (op/s)

The average number of overlapping write operations per second that are issued by the Global Mirror primary site. Some overlapping writes are processed in parallel and are excluded from this value.

This value applies to resources that are running IBM Storage Virtualize.

Peak Read Response Time (ms)

The worst response time measured for a read operation in the sample interval.

Peak Write Response Time (ms)

The worst response time measured for a write operation in the sample interval.

Global Mirror Secondary Write Lag (ms/op)

The average number of additional milliseconds that it takes to service each secondary write operation for Global Mirror. This value does not include the time to service the primary write operations.

You monitor the value of Global Mirror Secondary Write Lag to identify delays that occurred during the process of writing data to the secondary site.

Average number of additional milliseconds it took to service each secondary write operation for Global Mirror, beyond the time needed to service the primary writes

Overall Host Attributed Response Time Percentage

The percentage of the average response time that can be attributed to delays from host systems. This value includes both read response times and write response times, and can help you diagnose slow hosts and fabrics that are not working efficiently.

For read response time, the value is based on the time that it takes for hosts to respond to transfer-ready notifications from the nodes. For write response time, the value is based on the time that it takes for hosts to send the write data after the node responds to a transfer-ready notification.

Nonpreferred Node Usage Percentage

The overall percentage of I/O operations that are not directed against the preferred node for each volume in an I/O Group. There is a small performance penalty when I/O does not go to the preferred node for each volume.