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Concurrent migration of a disk device on host system to a SAN Replication device that represents a PPRC (peer-to-peer remote copy) pair.* Disclosure Number: IPCOM000233883D
Publication Date: 2013-Dec-26
Document File: 4 page(s) / 41K

Publishing Venue

The Prior Art Database


Usually migrating a disk device (representing a LUN) to PPRC device (representing a PPRC LUN) requires the device to be unconfigured and reconfigured on a host operating system. The following article discloses a method of migrating a disk device to PPRC device without requiring the device to be unconfigured and reconfigured thereby running the applications which uses the device uninterruptedly.

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Concurrent migration of a disk device on host system to a SAN Replication device that represents a PPRC (peer-to-peer remote copy) pair.*

PPRC(Peer-to-Peer Remote Copy) provides a replication mechanism for disaster recovery and business continuity. A pair of LUNs (Logical Unit Number) where one LUN is located in Site A (primary) and another LUN located in Site B (secondary) are designated as PPRC pair by the Storage Sub-systems. The storage sub-systems at locations A and B, have a replication path which is usually a high speed data link through which the replication happens. The two LUNs (primary & secondary) are replicated synchronously for each and every I/O write command (Synchronous PPRC). Synchronous PPRC pairs enables the data availability incase of any disaster at the primary site and also ensures data consistency.

The PPRC LUN pair can be configured by the host as a single disk device instance referred to in this article as SAN replication disk.

Let us consider a LUN detected and configured by the host and there is I/O happening on the LUN. If this LUN is made part of a PPRC pair on the storage subsystem, then user may want to migrate this disk device on the host corresponding to this LUN to a SAN Replication device which represents both the LUNs in the PPRC pair as paths to the same device instance.

The existing solutions require the device to be closed, unconfigured and reconfigured as a SAN Replication device. This requires stopping all the applications issuing I/O to the LUN, unmounting any filesystems created on top of this LUN. This can be very disruptive for the applications. In cloud environment where the users are served by the file systems on these LUNs it becomes very critical to do the migration operation in a non-disruptive way.

Disclosed is a method to migrate disk device on the host concurrently to a SAN replication device without interrupting the I/O to the LUNs. The migration process is transparent to the applications and hence will not have any impact on the applications doing I/O activity on the LUNs.

On the host operating system, a disk device has attributes which are configurable by the user. Disclosed is a method which updates the SAN Replication configuration policy concurrently and migrates the disk device to a SAN Replication device that represents both the LUNs in the PPRC pair as a single device.

In general, user executes a configuration method or a user command/application to modify the device attribute. The command or application is executed to modify the "SAN Replication configuration policy" attribute to "migrate_disk" which means that the same device name should be used to represent the PPRC LUN pair.


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When PPRC relationship is created storage sub-system creates a copy relationship identifier, which is same on both LUNs. The copy relation identifier is used to uniquely identify the LUNs in a PPRC pair. Usually the storage subsystem provides the copy relation identifier through...