Digital Equipment HSZ40, Справочное руководство

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2–78 SET unit-number
MAXIMUM_CACHED_TRANSFER=n
MAXIMUM_CACHED_TRANSFER=32 (Default)
The
MAXIMUM
_
CACHED
_
TRANSFER
switch allows you to set the largest transfer (in blocks)
to be cached by the controller. The controller will not cache any transfers over this size.
Valid values are 1–1024.
PREFERRED_PATH=THIS_CONTROLLER
PREFERRED_PATH=OTHER_CONTROLLER
NOPREFERRED_PATH (Default)
___________________________ Note ____________________________
All partitions on a container must be addressed through the same controller. If
you set
PREFERRED
_
PATH
for one partition, all partitions on that container will
inherit the same path.
____________________________________________________________
The
PREFERRED
_
PATH
switch allows you to balance I/O load by specifying the controller
through which the unit will be accessed. If you set
NOPREFERRED
_
PATH
for a unit, it can be
accessed through either controller.
The controllers only use the
PREFERRED
_
PATH
setting if they are in a dual-redundant
configuration. If one controller fails, all the devices are accessed through the remaining
controller, ignoring the
PREFERRED
_
PATH
setting.
___________________________ Note ____________________________
The
PREFERRED
_
PATH
and
NOPREFERRED
_
PATH
switches are valid only for HSZ
controllers in dual-redundant multiple bus-failover configurations. The preferred
path for units on dual-redundant HSZ controllers is determined by the first digit
in the unit number (the controller target ID) specified in the
ADD UNIT
command.
____________________________________________________________
When the failed controller is restarted, the drives automatically return to the controller
specified by the
PREFERRED
_
PATH
switch.
You can specify the
PREFERRED
_
PATH
switch on a single controller; however, the switch
will not take effect until you add a second controller and configure the two controllers for
dual-redundancy.
READ_CACHE (Default)
NOREAD_CACHE
The
READ
_
CACHE
switch allows you to enable or disable the use of read cache with a unit.
Read caching improves performance in almost all situations, so it is generally good to
leave it enabled. However, under certain workloads, like a backup, there may be a low