Thursday Morning Riddle

I’m a copy of files, because some might delete;
I’m the extras a cop calls for help on the street;
When a loud beeping truck makes a careful retreat;
And support for performers with voices or feet.

Who am I?

UPDATE: Riddle solved by Asher. See comments for answer.

2 Responses to “Thursday Morning Riddle”

  1. Asher Says:

    Backup

  2. Bill Says:

    BACK-UP is correct. Way to go, Asher!

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