Storage system with a point in time copy function

摘要

A computer storage system has a point in time copy function in which data stored in blocks of a master storage device 6 may be mapped to blocks of a shadow storage device 8 when a point in time copy is made with the bits of a bitmap 10 being used to indicate where data differs between the master and shadow storage device. A reduced size shadow storage device may be used with an address index pointing to locations in it. A selectable link may be provided between the shadow storage device and the host computer which produces point in time copies and a further selectable link between the shadow storage device and a second computer which is able to link to the shadow storage device to conduct analysis on data stored in it. Where a plurality of master volumes and shadow volumes are used, the making of a point in time copy of all of them can be simultaneous. Additional shadow storage devices and associated bitmaps can be provided with each master device whereby more than one point in time copy can be made.