Disclosed is a technique for reducing an amount of data transferred. A first indicator is maintained for each source block of data to indicate whether the source block of data has been updated in source storage since the source block of data was last transferred to target storage. A second indicator is maintained for each target block of data in target storage to indicate whether the target block of data has been updated in target storage since the target block of data was overwritten by a corresponding source block of data. When transferring data from the source storage to the target storage, each source block of data for which a first indicator has been set to indicate that the source block of data has been updated is transferred and each source block of data that corresponds to a target block of data for which a second indicator has been set to indicate that the target block of data has been updated is transferred.
Techniques are provided for performing a copy operation. An instant virtual copy operation is issued from a first portion of data to a primary mirroring portion of data, wherein the primary mirroring portion of data corresponds to a secondary mirroring portion of data, and wherein the primary mirroring portion of data and the secondary mirroring portion of data are in a mirroring relationship. The mirroring relationship is transitioned to a duplex pending state in response to determining that the mirroring relationship is in a full duplex state. When the mirroring relationship is in a duplex pending state, each block of data involved in the instant virtual copy operation is transferred from the primary mirroring portion of data to the secondary mirroring portion of data.
A file system may selectively perform redundancy consistency recovery and synchronization of mirrors and may store dirty file information in a log or journal that indicates the modification of a file. A file system may update saved dirty file information to indicate successful modification of data across mirrors and may keep track of redundancy consistency recovery information on a file-by-file basis or may track the redundancy consistency of portions of files. A file system may also instruct an underlying storage system not to track data modifications, possibly selectively for each I/O request. During synchronization the file system may synchronize its log and use saved dirty file information to determine files to be synchronized. A file system may selectively use file system logging for individual data modification requests and may expose an API allowing applications to specify a redundancy consistency mechanism.
