User`s guide

The maximum size you can specify for a volume is one-hundredth the size of
the volume; the minimum size you can specify is calculated with the following
formula:
disk_size (number_of_blocks)
___________________________
255*4096
For Files–11 On-Disk Structure Level 2 disks, the cluster size default depends
on the disk capacity; disks that are 50,000 blocks or larger have a default cluster
size of 3, those smaller than 50,000 blocks have a default value of 1.
When using the BACKUP/IMAGE command, use the following steps:
1. Enter the INITIALIZE/CLUSTER_SIZE=number-of-blocks device-name
command
2. Enter the BACKUP/IMAGE/NOINITIALIZE command
For further details, refer to OpenVMS VAX operating system software release
notes and other OpenVMS VAX documentation.
8.3.5.2 OpenVMS VAX V5.5–2 (and above)
The ‘‘unfavorable cluster size’’ error message does not occur with OpenVMS VAX
Versions 5.5–2 software or higher.
8.3.6 Shadow Set Operation with OpenVMS Systems
Timeout Value
For OpenVMS VAX operating system versions earlier than Version 6.0, timed-out
I/O requests to shadow set members can lead to member disks attached to HSJ40
array controllers being dropped from shadow sets. In some cases, this can lead to
host crashes. To avoid this possibility, Digital strongly recommends changing the
value of the SYSGEN parameter SHADOW_MBR_TMO to at least 120 (seconds)
for systems running operating system Version 6.0 and earlier. Version 6.1 of
OpenVMS (and later) avoids this problem by retrying timed-out operations to
shadow set members several times.
Shadow Set Members
Each physical device used in a OpenVMS operating system host-based shadow
set must be the same physical device type (for example, any of the controller
supported disk devices such as RZ25, RZ26, or RZ74 disk drives).
Note
You may not use transportable units as shadow set members.
A shadow set made of two or three RZ26 disk drives on one (or more) HSJ40
array controllers is valid. However, a mixture (in one shadow set) of RZ74 disk
drives and RZ26 disk drives is NOT valid and should not be attempted.
Because the HSJ and HSD30 array controllers report both disk drive types
as HSX00 (HSX00 is an example of a device type code), you must distinguish
between the two device types by determining the following attributes:
• Capacity. The capacity must be identical for all devices used within a single
shadow set.
8–8 Operating System Support