Quote:
The unavailable option provides for cases when a backup or copy cannot be found or has migrated offsite. A file that is marked UNAVAILABLE is not used in a restore or recover command. If the file is later found or returns to the main site, then you can mark it available again by using the available operand. Note that you do not need to allocate a channel of type maintenance for this operation.
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Note:
You must use a recovery catalog when executing change ... unavailable and change ... available. :D
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Also, in my past discussion with Oracle, I have heard this from a number of support personals of this solution. But the catch is what I have explained on my attachment earlier.