Dell Products Inc.

Gu Huang

Michael Ferrari

Kevin M Tobin

Akshay Kumar Srivastava

Sandeep Chandrashekhara

Nicholas W Von Hein

Direct Image Lookup (DIL) metadata is used to perform differential operation for snapshots and linked targets. Each snapshot contains metadata to store 'images' to perform direct lookup of user data for any part of any snapshot in the system. Metadata pages of DIL image data represent sets of tracks of data. Metadata pages of subsequent snapshots for the same sets of tracks are compared, and where there are no changes to a given metadata page for a given set of tracks between subsequent snapshot copies, the differential process is not run on the tracks associated with the metadata page. If a given metadata page associated with a set of tracks has changed between subsequent snapshots, the differential process is used to identify which tracks in the subsequent snapshot contain different data than the corresponding tracks of the previous snapshot. Similar differential processing also is implemented for relinked target devices.

Direct image lookup for determining quick differential for snapshots and linked targets

Memory management processes allocate and recycle pages of replication data pointer (RDP) metadata space in shared memory. When the RDP page currently allocated to an IO thread becomes full, that RDP page is released, and a new RDP page is allocated to the IO thread. The released page eventually becomes fragmented and is added to a list of RDP pages that are ranked based on partial fullness. An IO thread that needs a new RDP page is allocated a mostly empty RDP page from the ranked list, if such a page is available. Otherwise, a new completely empty RDP page is allocated to the IO thread. Use of the ranked lists reduces latency associated with allocation of new RDP pages. Contention between IO threads for RDP metadata space is reduced because each IO thread has exclusive rights to the free RDP metadata space in its currently allocated page.

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Chelmsford, MA, United States of America

Gu Huang