Comm Vault Systems, Inc.

Gaurav Yadav

Avinash Lakshman

In order to avoid writing duplicates of blocks of data into a storage platform, any virtual disk within the storage platform may have a de-duplication feature enabled. Or, all virtual disks have this feature enabled. For virtual disks with de-duplication enabled, a unique message digest is calculated for every block of data written to that virtual disk. Upon a write, these message digests are consulted in order to determine if a particular block of data has already been written, if so, it is not written again, and if not, it is written. All de-duplication virtual disks are written to a single system virtual disk within the storage platform. De-duplication occurs over the entire storage platform and over all its virtual disks because all message digests are consulted before a write is performed for any virtual disk. A read for a de-duplication virtual desk reads from the system virtual disk.

Global de-duplication of virtual disks in a storage platform

A computer receives a write request including an offset within a virtual disk. The computer writes the data block to a remote platform and calculates a hash value of the data. If the hash value does not exist in a first table of a block cache of the computer, the computer adds a pair to the first table: hash value/block cache data offset. Next, the computer adds a pair in a second table of the block cache: virtual disk offset of the data/hash value. A read request uses these tables to find the data in the cache without accessing the platform. The read consults the second table to find the hash value corresponding to the virtual disk offset of the block. The hash value is a key into the first table to find the block cache data offset of the data; the data is read from the cache.

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Mountain View, CA, United States of America

Gaurav Yadav