The only way to restore this back is to datacopy the backup back to the original multi-stream capable device. However it was noted that data copied backupset can't be datacopy again. The following steps will allow Netvault to perform a datacopy on the saveset again.
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Modify the Archive flag to FALSE in database.This can be done in two ways as follows:
Using GUI
Launch the pgAdmin3 (installed in <Netvault_Install_Dir>\pgsql\bin )
Connect to the Netvault database and go to netvault_mediamanagement database.
Go to schema->Public→medmgrbackuprecord table.
Fire update command or edit in view records the barchive column to FALSE respective to jobid.
Using Command Prompt
Open command prompt and change directory to <Netvault_Install_Dir>\pgsql\bin
Fire up the below command and replace XXX with phase 2 backup jobid in below command line.
SQL Query
psql -U postgres -W -p 51486 -d netvault_mediamanagement -c "UPDATE \"medmgrbackuprecord\" SET \"barchive\"=FALSE WHERE \"jobid\"=XXX"
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After this, perform a datacopy from the tape saveset to a RDA device or smartdisk and perform the restore from there.