Importance

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Abstract

Non-disruptive data migration moves are performed form a source DASD to target DASD in a data subsystem. Both source and target DASDs comprise a cache and a nonvolatile store (NVS). Relative to the host, the target DASD generally operates as a source, managing requests for access to source DASD data by issuing I/O requests to the source DASD. First, the target DASD initiates a background data transfer, where data is copied from the source DASD to the target DASD preparing the target DASD to replace the source DASD. The data transfer includes copying data items directly from the source DASD's cache to that of the target DASD's cache, as well as copying data items from the source DASD's NVS to the target DASD's NVS. During background data transfer, the host can still perform data access operations, such as reads and writes, using the target DASD. Namely, for data already copied from the source DASD to the target DASD, the host reads this data from the target DASD. Host requests to read data not yet copied to the source DASD causes staging of the data from the source DASD to the target DASD. For host write requests, the data to be written to the target DASD, if no source data is needed to complete the write. To satisfy host write requests requiring data not yet copied from the source DASD, the data is copied from the source DASD to the target DASD.

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