Hello there,
Backup to disk storage goes into offline due to various reasons ( usually environment specific ) :-
Device is offline means that Backup Exec has lost communication with the device.
a). Check physical connectivity with disk enclsoure ( whether it is DAS, SAN or iSCSI )
b). Check if we have enough space on the B2D volume
c). As you mentioned "The storage of our backup is in different Server" ) it means... B2D is configured over network ? Is network connection consistent ? Check windows system and application event logs by looking at windows system and application event logs will hep us to isolate the issue. You may also need to look at adamm log to get info related to offline B2D, here is link to how to read the ADAMM.LOG file, and what various errors mean within the log.
https://www.veritas.com/support/en_US/article.000042269
d). You may also try running Backup Exec Backup to Disk test tool (B2Dtest.exe), it is a stand-alone tool intended to test the basic functionality of a device as it relates to being used as a Backup-to-Disk device in Backup Exec, here link about tool and download link :-
Information regarding the Backup Exec Backup to Disk Test Tool - B2Dtest.exe
https://www.veritas.com/support/en_US/article.000037869
Backup Exec Backup-to-Disk Test Tool (B2DTest_64bit.exe) - 64 Bit Version
https://www.veritas.com/support/en_US/article.100036594
You may also refer these technote which may or may not relevant to your issue :-
The alert "The Backup-to-Disk device is offline" appears while performing a backup to a Backup to Disk folder using Backup Exec for Windows Servers.
https://www.veritas.com/support/en_US/article.TECH54598
Backup-to-Disk storage is offline after database maintenance
https://www.veritas.com/support/en_US/article.000019712
Hope this will help.
