MDisk Groups - Workload Activity report

Shows the workload activity of managed disk (MDisk) groups. You can use the information that the report provides to investigate which MDisk groups are being underused or overused.

Restriction: This report applies only to SAN Volume Controller and Storwize® systems.

Reporting periods

The name of the storage virtualizer, the date filter such as Last 7 days, and the reporting period are displayed in the report.

Retention of report data

If you remove an MDisk group or a VDisk, the daily data that is collected for reports is retained for a configurable period. The default is 90 days. If you run a report after the data retention period expired, the daily data for the MDisk group or the VDisk is unavailable.

Read I/O rate capability

To estimate the read I/O rate capability of an MDisk group, you must set the back-end pool properties of MDisk groups.

If you do not set the back-end pool properties of an MDisk group:

Not Set is displayed in the MDisk Group Read I/O Rate Capability column
Not Available is displayed in the MDisk Group Read I/O Rate Availability column

If the read I/O rate capability of an MDisk group is less than the maximum read I/O rate of the MDisk group, negative values are displayed in the report.

Charts

The maximum length of an MDisk group, VDisk, or storage resource group name in charts is 25 characters. Names that are longer than 25 characters are truncated. To indicate that a name is truncated, an ellipsis (...) is appended to the name. For example, if the name of an MDisk group is myverylongmanageddiskgroupname123 in a chart, it is truncated and displayed as myverylongmanageddiskgroupname...

Two charts are displayed:

Most Active MDisk Groups
Most Available MDisk Groups

Most Active MDisk Groups

For each MDisk group two bars are used:

A yellow bar that shows the average activity value
A red bar that shows the maximum activity value

To calculate the average activity value of an MDisk group, the following formula is used:

average(maximum_read_I/O_rate ÷ read_I/O_rate_capability)

To calculate the maximum activity value, the following formula is used:

maximum(maximum_read_I/O_rate ÷ read_I/O_rate_capability)

In this sample excerpt of report output for mdiskgroup1, the values that are required to calculate average and maximum activity values are provided.


MDisk Group Report Date	MDisk Group Read I/O Rate Capability (ops/s)	MDisk Group Max Read I/O Rate (ops/s)
Dec 6 2011	331	216.77
Dec 7 2011	331	256.40
Dec 8 2011	331	270.87

The average activity value of an MDisk group is calculated as follows:

For each report in the MDisk group, the value in the MDisk Group Max Read I/O Rate column is divided by the value in the MDisk Group Read I/O Rate Capability column:
```
216.77 ÷ 331 = 0.65
256.40 ÷ 331 = 0.77
270.87 ÷ 331 = 0.81
```
The result of the operation for each report is added:
```
0.65 + 0.77 + 0.81 = 2.23
```
To get the average value, the total is divided by the number of days that are specified in the date range. For example, if the reporting period spans 3 days, the total is divided by 3.
```
2.23 ÷ 3 = 0.74
```

The maximum value of an MDisk group is calculated as follows. For each report in an MDisk group, the value in the MDisk Group Max Read I/O Rate column is divided by the value in the MDisk Group Read I/O Rate Capability column:

216.77 ÷ 331 = 0.65
256.40 ÷ 331 = 0.77
270.87 ÷ 331 = 0.81

In this sample, the maximum value is 0.81.

Most Available MDisk Groups

For each MDisk group two bars are used:

A blue bar to represent minimum values
A red bar to represent average values

In this sample excerpt of report output for mdiskgroup2, the values that are required to calculate minimum and average availability values for MDisk Groups are provided.


MDisk Group Report Date	MDisk Group Read I/O Rate Availability (ops/s)
Dec 6 2011	435.41
Dec 7 2011	560.92
Dec 8 2011	480.95

The minimum value of an MDisk group is calculated as follows:

For all of the reports for an MDisk group, the lowest value in the MDisk Group Read I/O Rate Availability column is used. In this sample, the lowest value for mdiskgroup2 is 435.41.

The average value of an MDisk group is calculated as follows:

For each report in an MDisk group, the values in the MDisk Group Read I/O Rate Availability column are added:
```
435.41 + 560.92 + 480.95 = 1477.28
```
To get the average value, the total is divided by the number of days that are specified in the date range. (For example, if the reporting period spans 3 days, the total is divided by 3.)
```
1477.28 ÷ 3 = 492.42
```

In this sample, the average value is 492.42.

The number of MDisk groups in a storage virtualizer determines how many MDisk groups are displayed in each chart, as shown in the following table.


Number of MDisk groups in the storage virtualizer	Number of MDisk groups in the Most Active MDisk Groups chart	Number of MDisk groups in the Least Active MDisk Groups chart
≥ 10	5	5
9	5	4
8	4	4
7	4	3
6	3	3
5	3	2
4	2	2
3	2	1
2	1	1
1	1	0

Tip: Click the bar that represents an MDisk group in a chart to open the MDisk Group - VDisk Workload Activity Details Report. Alternatively, you can click the name of the MDisk group in the report.

Threshold values

The names of the threshold values in the report that are used to monitor workload activity for MDisk groups are:

Actual Size Threshold
Read I/O Rate Threshold
Max Read Response Time Threshold
Max Write Response Time Threshold

Threshold values are set during installation. If a threshold value is changed during a reporting period, the original value and the new threshold value are displayed as minimum and maximum values. If, for example, the value of the actual size threshold is changed during a reporting period from 50% to 60%, the name of the column is changed to MDisk Group Available Size < Actual Size Threshold of {50 - 60%}. The convention that is used to represent a threshold value is a number followed by the percent sign and enclosed in brackets: {%}. When the report is run, the variable value is replaced with the threshold value. To calculate whether read or write response time thresholds are exceeded, the following formula is used:

(maximum_response_time_value × maximum_response_time_threshold_value)÷ 100.

The result is converted from seconds to hours and minutes, and displayed in the report. Read and write response times are sampled at 5-minute intervals over a 24-hour period.

Report output

For each MDisk group, the following information is provided:

MDisk Group: The name of the MDisk group.

MDisk Group Report Date: The date that the data was collected for the report.

MDisk Group Capacity Status

If the storage capacity that is allocated is less than the actual storage capacity, a status value of OK is displayed. If the storage capacity that is allocated is more than the actual storage capacity, a status value of Warning is displayed. The actual capacity of the MDisk group is calculated as follows:

 (mdisk_group_real_capacity_value ÷ mdisk_group_capacity_value) × 100

MDisk Group Capacity (GB): The total storage capacity in GB of all of the disks in the MDisk group.

MDisk Group Real Capacity (GB): The total amount in GB of real storage capacity in the MDisk group.

MDisk Group Free Space (GB): The total amount of remaining capacity in GB that can be allocated to increase the size of an existing VDisk, or allocated to an additional VDisk.

MDisk Group Available Size < Actual Size Threshold of {%}: If the amount of storage space that is available for allocation to VDisks is less than the actual size threshold, Yes is displayed in the column. If the amount of storage space that is available for allocation to VDisks is more than the actual size threshold, No is displayed in the column.

MDisk Group Read I/O Rate (ops/s): The read I/O rate of the MDisk group in operations per second.

MDisk Group Read I/O Rate Capability (ops/s): The read I/O capability rate of the MDisk group in operations per second.
Tip: To find out how the read I/O capability rate is calculated, see Read I/O capability formula

MDisk Group Max Read I/O Rate (ops/s): The maximum read I/O rate of the MDisk group in operations per second.

MDisk Group Read I/O Rate Availability (ops/s): The difference between the read I/O capability rate and the maximum read I/O rate in operations per second.

MDisk Group Read I/O Rate Availability < Read I/O Rate Capability Threshold of {%}: The availability rate for read I/O operations is compared with the read I/O rate capability threshold. If the availability rate for read I/O operations is less than the read I/O rate capability threshold, Yes is displayed in the column. If the availability rate for read I/O operations is more than the read I/O rate capability threshold, No is displayed in the column.

MDisk Group Max Read Response Time (ms/op): The maximum read response time in milliseconds per operation.

MDisk Group Max Read Response Time Threshold of {%} Exceeded By (hr.:min.): The number of hours and minutes that the maximum read response time threshold is exceeded over a 24 hour period.

MDisk Group Average Read Response Time (ms/op): The average read response time in milliseconds per operation.

MDisk Group Max Write I/O Rate (ops/s): The maximum write I/O rate in operations per second.

MDisk Group Max Write Response Time (ms/op): The maximum write response time in milliseconds per operation.

MDisk Group Max Write Response Time Threshold of {%} Exceeded By (hr.:min.): The number of hours and minutes that the maximum write response time threshold is exceeded over a 24 hour period.

MDisk Group Average Write Response Time (ms/op): The average write response time in milliseconds per operation.

MDisk Group Average Write I/O Size (KB): The average size of write I/O operations in KB.