技师想要一台备用发动机以防万一。
The technician wanted to keep an auxiliary engine handy just in case.
两台40马力的压缩机运行，另外还有一台备用。
Two 40 HP screw compressors in operation, plus one new standby compressor provided.
例如，有些客户可能会在一台备用机器上建立一个日志传送环境。
For example, some customers may choose to set up a log shipping environment on a standby machine.
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