Playback and Recording : Record Setup : Record Modes : Destructive Record Mode

Destructive Record Mode
In Destructive Record mode, recording over existing clips replaces the original audio permanently, which allows you to keep disk use to a minimum. However, if you have sufficient drive space, it is usually best to use Pro Tools in Nondestructive Record mode, to avoid losing any previously recorded material.
When defining the record range and setting pre- and post-roll, Destructive Record mode works the same as Normal (Nondestructive) mode.
Unlike the other record modes, it is not possible to cancel or undo record takes when using Destructive Record mode (see Canceling a Record Take).
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In Destructive Record mode, the waveform overview is not redrawn until you stop recording.
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Destructive recording is not supported with AudioSuite rendered clips with handles. You can consolidate such clips if you need to use Destructive Record mode.