The maintenance --filesystem --start_scan verify_data" will place the DR in Maintenance mode and the filesystem in read-only. Backups will not be permissible during this check. More details below.
When in its Maintenance mode, the filesystem is in a read-only state, and the system runs the following maintenance-based operations:
If the filesystem check finds issues, you can choose to make repairs (using Confirm Repair Filesystem) or ignore the detected issue (using Skip Repair Filesystem), at which point the system switches back to Operational mode.
NOTE: If the Filesystem Check detects any repairable files, it generates a Repair Report that identifies these reported files. The Maintenance Mode progress bar halts at the Completed Generating Repair stage, and remains in Maintenance mode until you click Confirm Repair Filesystem. The DR Series system does not advance to the Switching to Operation Mode stage until the filesystem repair is completed.