Gbak vs nBackup: Which minimizes downtime for a small Firebird app migration?

Goal

To move a lightweight Firebird application to a new server while keeping the database online for as long as possible.

Constraints

• Final cut‑over must be brief enough that users experience no service interruption.
• Backup method should preserve all schema and data without requiring extensive post‑restore processing.
• Version compatibility between source and target Firebird installations must be maintained.

Unresolved Decision

Should the migration use the logical Gbak tool, which offers portability but requires a full restore, or the physical nBackup tool, which restores faster but may be affected by OS differences and incremental windows?

Specific Questions

1. What is the typical downtime window when restoring a 10‑GB database with Gbak versus nBackup on the same Firebird version?
2. Can nBackup incremental backups effectively reduce the final cut‑over period for a small database, and if so, by how much?
3. What ODS or version mismatches should be anticipated when restoring an nBackup image from a 3.0 source to a 4.0 target, and how do they impact downtime?