Fujitsu BS2OSD Manuale Utente

Page 19

Dynamic I/O load distribution for disks on the FC channel of

the S server (DPAV)

Only one I/O can be executed at any particular time on a disk.

If several applications with a large number of I/Os use the same

disk, this can lead to high wait times.

Until now, static PAV (Parallel Access Volume) has been used on

S servers since BS2000/OSD-BC V5.0 to alleviate this problem.

The function allows multiple concurrent accesses to one logical

device.

With PAV, several device addresses (alias devices) are assigned

to one logical (base) device on the same controller, thus

allowing multiple I/O orders to be started concurrently via

the base and alias devices.

PAV on the FC channel is a pure software solution that can be

operated without intervening in the Symmetrix controller. To do

this, BS2000 uses the fact that disks on the FC channel can

still accept I/O orders if an I/O is already active.

Static PAV assigns the alias devices statically to the base

device and therefore requires predictive planning of device

utilization.

Dynamic PAV (IORM DPAV function) assigns the alias devices

autonomously to the volumes that would profit most from them.

For devices connected via type FC, DPAV switches an alias

device from the current base device to another base device by

dynamically changing the I/O configuration.

In VM2000 operation, DPAV must be activated for each guest

system in which DPAV is to be active.

Note: /START-VM cannot be used during dynamic I/O configuration

changes on S servers while operating under VM2000.

When using the IORM DPAV function, dynamic I/O reconfiguration

can be called at any time, thus disrupting /START-VM

For this reason, as of VM2000 V9.0 with /START-VM and active

dynamic I/O reconfiguration the system waits a maximum of 15

seconds for the I/O reconfiguration to be completed. If the I/O

reconfiguration takes longer, /START-VM is rejected.

The following restrictions apply when using HIPLEX AF under

VM2000 < V9.0:

- If the "warm standby" scenario is used, the DPAV function must

be deactivated on all virtual machines of the standby system.

- When monitoring the guest system with VM2000 resources via the

live monitor while using DPAV, RESTART-AFTER-STOP=*NO must be

set in the ADD-VM2000-MONITORED-SYSTEM statement.

Optimized load distribution in CentricStor operation (DDAL)

This function can be activated but the controlling intervention

will only be implemented in future BS2000/OSD-BC versions. DDAL

must be activated on all guest systems and the monitor system

for IORM to be able to take control in VM operation.