=;The OpenVMS Frequently Asked Questions (FAQ)D

The OpenVMS Frequently Asked Questions (FAQ)



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B

15.6.8 Details on Volume Shadowing?



EThis section contains information on host-based volume shadowing; on 9the disk mirroring capabilities available within OpenVMS.c

15.6.8.1 Does volume shadowing require a non-zero allocation classes?



BYes, use of host-based Volume Shadowing requires that the disk(s) 6involved be configured in a non-zero allocation class.

<Edit SYS$SYSTEM:MODPARAMS.DAT to include a declaration of anHnon-zero allocation class, such as setting the host allocation class to the value 7:

 

"
ALLOCLASS = 7 




$Then AUTOGEN the system, and reboot.

HYou should now be able to form the shadow set via a command such as the following:

 

"
=$ MOUNT dsa1007: /SHADOW=($7$dkb300:,$7$dkb500:) volumelabel 




CWhen operating in an OpenVMS Cluster, this sequence will typically @change the disk names from the SCSNODE prefix (scsnode$dkann) toI the allocation-class prefix ($7$dkannn). This may provide you with the H opportunity to move to a device-independent scheme using logical name H constructs such as the DISK$volumelabel logical names in your startup D and application environments; an opportunity to weed out physical  device references.

FAllocation class one is used by Fibre Channel devices; it can be best Fto use another non-zero allocation class even if Fibre Channel is not /currently configured and not currently planned.




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