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*4 Dynamic I/O load distribution for disks on the FC channel of
*4 the S server (DPAV)
*4 Only one I/O can be executed at any particular time on a disk.
*4 If several applications with a large number of I/Os use the same
*4 disk, this can lead to high wait times.
*4 Until now, static PAV (Parallel Access Volume) has been used on
*4 S servers since BS2000/OSD-BC V5.0 to alleviate this problem.
*4 The function allows multiple concurrent accesses to one logical
*4 device.
*4 With PAV, several device addresses (alias devices) are assigned
*4 to one logical (base) device on the same controller, thus
*4 allowing multiple I/O orders to be started concurrently via
*4 the base and alias devices.
*4 PAV on the FC channel is a pure software solution that can be
*4 operated without intervening in the Symmetrix controller. To do
*4 this, BS2000 uses the fact that disks on the FC channel can
*4 still accept I/O orders if an I/O is already active.
*4 Static PAV assigns the alias devices statically to the base
*4 device and therefore requires predictive planning of device
*4 utilization.
*4 Dynamic PAV (IORM DPAV function) assigns the alias devices
*4 autonomously to the volumes that would profit most from them.
*4 For devices connected via type FC, DPAV switches an alias
*4 device from the current base device to another base device by
*4 dynamically changing the I/O configuration.
*4 In VM2000 operation, DPAV must be activated for each guest
*4 system in which DPAV is to be active.
*4 Note: /START-VM cannot be used during dynamic I/O configuration
*4 changes on S servers while operating under VM2000.
*4 When using the IORM DPAV function, dynamic I/O reconfiguration
*4 can be called at any time, thus disrupting /START-VM
*4 For this reason, as of VM2000 V9.0 with /START-VM and active
*4 dynamic I/O reconfiguration the system waits a maximum of 15
*4 seconds for the I/O reconfiguration to be completed. If the I/O
*4 reconfiguration takes longer, /START-VM is rejected.
*4 The following restrictions apply when using HIPLEX AF under
*4 VM2000 < V9.0:
*4 - If the "warm standby" scenario is used, the DPAV function must
*4 be deactivated on all virtual machines of the standby system.
*4 - When monitoring the guest system with VM2000 resources via the
*4 live monitor while using DPAV, RESTART-AFTER-STOP=*NO must be
*4 set in the ADD-VM2000-MONITORED-SYSTEM statement.
*4 Optimized load distribution in CentricStor operation (DDAL)
*4 This function can be activated but the controlling intervention
*4 will only be implemented in future BS2000/OSD-BC versions. DDAL
*4 must be activated on all guest systems and the monitor system
*4 for IORM to be able to take control in VM operation.