Backups
Object-storage backup vs sync: a second copy needs history and recovery intent
Copying files into an S3 bucket can be useful, but it does not automatically create a backup. A mirror that immediately propagates deletion or corruption may give you a second location containing the same damaged state.
Sync tries to make two views agree
A synchronization tool commonly compares source and destination and applies changes until they match. That is useful for distribution and replication, but the desired end state may include deleting destination objects that disappeared at the source.
If the source was deleted accidentally, a perfectly successful sync can reproduce the mistake.
Backup preserves recovery points
A backup process normally has a retention model that lets an operator choose an earlier point in time. It may use unique object names, manifests, snapshots or object versions to preserve history.
The catalogue and metadata that describe those recovery points are part of the backup. Raw object bytes alone can be difficult to reconstruct without them.
Consistency matters for applications
Copying database files while the database is actively changing can produce an unusable set of objects. Application-aware backup tools coordinate snapshots, dumps or transaction logs before sending the result to object storage.
The object destination cannot repair an inconsistent source capture after the fact.
Deletion policy should be explicit
Decide whether source deletion should remove the object immediately, after a retention period or never automatically. Configure lifecycle rules and backup software to implement that choice explicitly after reviewing the default behaviour.
A retention policy also needs a way to clean up old data eventually so a fixed-capacity service does not fill permanently.
Test the restore path
Pick a file or dataset, delete or alter the source, then recover the earlier version using the documented procedure. A sync job may pass this test only if another history mechanism exists.
Call the system a backup when it has demonstrated recovery behavior, not simply because the destination is remote.