How can I monitor and manage the Vtape backstore process?

Products

• Vtape Virtual Tape System

Issue/Introduction

What methods are available for monitoring and managing the Vtape backstore process? 

Environment

Component:Vtape

Resolution

The SVT1 Display Groups console command can be used to get backstore related information:

For example:

/SVT1 D G                                                           

SVT1X0300I Display Group Information 152                           

 Max Drives=0005, USS=0000                                         

 Thresholds Warning=090%, Hold=000%, Release=000%                  

 Schedule=(09:00-16:59), Disabled                                  

 Dasd cache utilization 01222892/00859432/00107459 InUse=61%       

                                                                   

  Group Status  Queue  #Vols  MB.Used MB.Alloc Dasd% MB.Thold Prty 

  ----- ------- ------ ----- -------- -------- ----- -------- ---- 

   01.S  Hold   All     1131   124016   125139   10%     2000  1.8 

   01.M  Hold   All      102   119492   119594   10%     2000  1.8 

   01.L  Hold   All      386    38168    38552    3%     2000  1.8 

   02.S  Hold   All      190    25372    25562    2%     2000  1.8 

   02.M  Hold   All        8     1932     1940    0%     2000  1.1 

   02.L  Hold   All      286   417340   417615   34%     2000  1.8 

  Totals:               2103   726320   728402   60%               

  An asterisk (*) in the Status column indicates an automated queue

 SVT1X0100I Command Complete                

The header section documents the current settings of various parameters that affect how the Backstore Engine operates.

In the example above:

1. The maximum number of drives that the Backstore Engine is allowed to use at one time is five (Max Drives=0005). 
2. There are no Unix System Services mount points defined to the Backstore Engine (USS=0000).
3. The CacheWarningThreshold is set to 90% (Warning=090%).
4. The CacheAutoHoldLowThreshold is set to 0% (HOLD=000%).
5. The CacheAutoReleaseHighThreshold is set to 0% (Release=000%).  At setting of 0 indicates that Backstore Automation, the automatic release and hold of the Backstore Groups Queues, is not active.  The queues must be manually released and held with console commands. 
6. The CacheAutomationSchedule is set to 09:00-16:59 (Schedule=(09:00-16:59)), but is not in use since Backstore Automation is not active.
7. Backstore Automation has not been configured (Disabled).
8. The DASD cache currently has 1,222,892 MBs of storage.  859,432 MBs of that storage is currently populated with data.  107,459 MBs of the populated data has been Backstored and can be freed (deleted) when needed.  The percentage of storage that has not been Backstored and cannot be free or reused is 61% (InUse=61%).
9. The table displays only those queues which have data in them to be Backstored.  Currently six queues have data to be Backstored.  The status of these groups is all HOLD so nothing will be Backstored.  Since the Backstore Automation status is DISABLED, these queues must be manually released with a console command (see SVT1 SET BACKSTORE,RELEASE console command).  If these queues were set up for automation, they status value would be prefaced with an asterisk (*) as in *HOLD.  A queue that is released, but is not currently Backstoring will have a status of RLSE or *RLSE.  A queue that is actively Backstoring will have a status of ACT(n) where n is the number of Backstore subtasks.  ACT(2) would indicate that two subtasks are active for this queue so each task will have its own drives and tapes mounted.  If this queue has Duplexing turned on, each task will have 2 drives in use for a total of 4.
10. The table also tells you how many Virtual Volumes are queued in each queue and how much of the cache they are consuming along with how much data there is to be Backstored (MB.Used) and how much DASD space is being consumed (MB.Alloc).
11. The MB.Thold column displays the setting of the MB_THRESHOLD parameter in the Groups Definitions.  This value is used by the Backstore Engine to determine the number of subtasks that should be started for a queue.  If the value is at the default of 2000 MBs and there are 5000 MBs of data to be Backstored in the queue, 5000 is divided by 2000 and rounded down to 2.  The Backstore Engine will try to start two subtasks to Backstore this queue without exceeding the Maxdrives settings.  Lowering the MB_THRESHOLD value will increase the amount of concurrent Backstoring for a queue, raising the value will decrease the amount of concurrent Backstoring for a queue.  Since each subtask uses its own drives and tapes, increasing concurrency will increase drive and tape usage.  Decreasing concurrency will reduce drive and tape usage. 

If you issue this command once an hour or once every 30 minutes, you can use the output to track over time what the Backstore Engine address space is doing, which queues have data in them, how much data is in each queue, which queues are active, and how much cache is in use.

The SVT1 Display Group,All version of the console command will display all the queues regardless of whether there is any data queued in them.  This version of the command might be more useful for use with console automation software since it will always contain the same number of output lines and will always display the queues you are interested in.