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A data facility Hierarchical Storage Manager volume to which all but the latest backup version of a data set are mover when more space is needed on a DASD daily backup volume or to which all valid versions are moved when a tape backup volume is recycled.; 一种数据设施分层存储管理卷。当在直接存取存储设备的日常备份卷上需要更多的空间时,则除了最近生成的数据集备份版本外,其它全部内容将被移到溢出 备份卷;当一个磁带备份卷被循环重新使用时,则该卷的全部的有效版本被移到溢出备份卷。