An administrator is migrating their old cloud tier-enabled Data Domain to a new PowerProtect DD appliance with cloud tier. During migration, the administrator recognizes that file system cleaning on the source system is not possible. What is the most likely cause of this behavior?

During a data migration process, especially one involving a cloud tier, the source PowerProtect DD system is placed into a "restricted mode." This mode is a protective measure to ensure data consistency and prevent any modifications to the filesystem's metadata or data layout while it is being read and transferred to the new system. In restricted mode, several administrative operations, including filesystem cleaning (garbage collection), are disabled. This prevents the source system from reclaiming space from deleted files that might still be queued for migration.

A. This is too broad. While many activities are restricted on the source, the destination system is active and receiving data.
C. The filesystem is not disabled; it must remain active and readable for the migration process to access and copy the data.
D. This is inaccurate. Not all activities are restricted; for example, reading data for migration is a primary activity that is allowed.

- Dell PowerProtect DD OS 7.13 Administration Guide, Page 649, "Migration considerations," explains that during the migration commit phase, the source system enters a restricted mode where operations like cleaning are disallowed.

- Dell PowerProtect DD Cloud Tier Implementation Guide, (relevant sections on migration), implicitly supports this by detailing the read-only nature of the source filesystem during transfer to maintain data integrity, which aligns with the behavior of restricted mode.