DASD Buffer Shortage

As shown in the following figure, the SVTnD0908I message is sent every minute after the DASD buffer threshold is reached, and continues to be sent until the DASD buffer pool is relieved (SVTnD0912I). If the DASD buffer reaches 100 percent utilization, all the Virtual Devices will stop and message SVTnP0420W or SVTnV0432E or both are issued. Virtual Device activity automatically resumes as soon as DASD buffer space is available.

The following illustration is the first example of SDSF SYSLOG:

SVT1 D G,D SVT1X0300I Cache Size (MB) 00013000/00012840/00002400, In Use=080% Max Drives=0006, Thresholds Warning=075%, Hold=020%, Release=065% Schedule=(00:00-15:00,15:05-19:59,20:15-23:59), State=On Group Status Queue #Vols MB.Used MB.Alloc Dasd% MB.Thold Prty ----- ------- ------ ----- -------- -------- ----- -------- ---- 11.S *Act(2) Local 2 800 800 6% 1000 3.0 Global 5 1852 1880 14% 11.M *Act(1) Local 2 652 680 5% 1000 3.0 Global 1 400 400 3% 33.L *Rlse Local 0 0 0 0% 3000 1.1 Global 4 832 880 7% 51.S *Act(1) Local 1 400 400 3% 12000 1.0 Global 4 912 960 7% 51.L *Act(1) Local 1 400 400 3% 12000 1.0 Global 1 400 400 3% Totals: 21 6648 6800 52% SVT1X0100I Command Complete *SVT1D0908I SVTS Cache Shortage - 080% Utilization Reached *SVT10432W 3504,100556, Cache shortage, Reply R(etry) or C(ancel) *SVT10432W 3501,100557, Cache shortage, Reply R(etry) or C(ancel) CTS014 IEF23E K 3507,100544,PVT,RIDOSDI4 IEF234E K 3507,100544,PVT,RIDOSD14 IEF404I RIDOSD14 - ENDED - TIME=17.56.48 *SVT1D0908I SVTS Cache Shortage - 077% Utilization Reached SVT1 REFRESH=OPTONS <<--- Changed CacheWarningThreshold in parmlib SVT1X0100I Command Completed Successfully SVT1D0912I SVTS Cache Shortage Relieved

The DASD buffer may reach 100% utilization in the following conditions:

Insufficient DASD buffer space allocated to handle CA Vtape activity.
Note: For information on how to properly size the DASD buffer, see the chapter “Cache Management” in the Configuration Guide.
Insufficient physical drives to Externalize the Virtual Volumes to physical tape.
The Primary and Failover Externalization Servers are not active or Subgroup Automation was not set for the group or subgroups queues using most of the DASD buffer. Corrective actions include the following:
- Execute SVTn D G on the CA Vtape subsystem defined to run the primary Externalization Server. Is Release > 0? (Second line of the SVTn D G display). If so, this is the Externalization Server.
- Is Warning <= Release? If so, you are receiving the Warning Cache Shortage message before Subgroup Automation was scheduled to start the Externalization Server. Either modify parmlib attributes CacheWarningThreshold or CacheAutoReleaseHighThreshold, or check other CA Vtape subsystems because this subsystem might not be set up as the primary Externalization Server but the secondary instead.
- Is Release >= In Use? If so, that means Subgroup Automation was not scheduled to start yet. Temporarily release the queues by issuing SVTn SET BACK=-R,G=*, and after the DASD buffer utilization is back to normal issue SVTn SET BACK=T,G=* to reset Subgroup Automation to the parmlib specified values. Modify parmlib attribute CacheAutoReleaseHighThreshold to a more suitable value.
- Is the State On? If not, the Externalization Server is Off based on schedule. To override the schedule and release the queues execute a SVTn SET BACK=-R,G=* command.
- If the State is On, but the group or subgroup queue holding most of the data is on Hold without a leading * in front of the Status, it is because the queue is not automated. Either temporarily automate it by executing the SVTn SET BACK=A,G=xx or just release it by executing SVTn SET BACK=R,G=xx.

Other corrective action includes the following steps:

Run SVTSUTIL RECLAIM.
Note: For information on how to run the SVTSUTIL RECLAIM command, see the chapter “SVTSUTIL Batch Commands.”
Execute the SVTn D B console command to verify that the Backstore can allocate and write over the physical tapes.
If possible, let the Backstore Engine use more physical tapes by issuing the SET MAXDRIVES=nn console command.
Reply R to any outstanding SVTn0432W message.