Browse Prior Art Database

Block Level N-Way IP Mirroring

IP.com Disclosure Number: IPCOM000011538D
Original Publication Date: 2003-Feb-28
Included in the Prior Art Database: 2003-Feb-28
Document File: 3 page(s) / 77K

Publishing Venue

IBM

Abstract

Disclosed is an application of an N-way tree data structure in an IP networking environment to achieve a self-adapting N-way recursive data redundancy solution. The tree is constructed of iSCSI mirror volumes. Each tree root or subtree root is a system with a RAID 1 volume. The RAID 1 volume consists of the mirror primary, backed by local SCSI storage, and (N - 1) mirror secondaries, each an iSCSI volume mapped in across the IP network. The (N - 1) secondaries are leaves of the tree or subtree roots for further brancing of the tree. Adding intelligence to the iSCSI mirrors allows the N-way mirror tree to become a policy-based self-healing data redundancy tree. The design goals are discussed along with how they are met, and a Figure illustrates the architecture of the system.

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Block Level N-Way IP Mirroring

Disclosed is an application of an N-way tree data structure in an IP networking environment to achieve a self-adapting N-way recursive data redundancy solution. The tree is constructed of iSCSI mirror volumes. Each tree root or subtree root is a system with a RAID 1 volume. The RAID 1 volume consists of the mirror primary, backed by local SCSI storage, and (N - 1) mirror secondaries, each an iSCSI volume mapped in across the IP network. The (N - 1) secondaries are leaves of the tree or subtree roots for further brancing of the tree. Adding intelligence to the iSCSI mirrors allows the N-way mirror tree to become a policy-based self-healing data redundancy tree.

Application technologies include:

Ubiquity/reliability of IP networking technology. This ensures the network

underpinning the technology is readily available. Open-platform iSCSI storage target products such as Linux systems, which allow

building the self-adapting intelligence into the target system. Simple (to configure) software RAID 1 mirroring achievable in most operating

systems.

The design goals (and how they are met) of the system include:

Easy setup: Configuration consists of (1) mapping the iSCSI volumes, a simple

matter of installing an initiator and logging in to the iSCSI target, and (2) configuring the software RAID 1 in the operating system, which is 1 extra step during formatting a volume. Distributed failure tolerance - If the local system fails, the network half of the

mirror (and N-way replicas of it) is accessible by logging in to the iSCSI target from another machine and mapping it as a volume. Minimal performance degradation. OS-based RAID 1 is synchronous mirroring,

thus writes are delayed by the need for them to commit to the network half of the mirror. Combining Gigabit and faster Ethernet technology with sufficient battery-backed caching at the iSCSI target allows commit delay approaching local disk.

Recursive self-adapting failure tolerance. Building intelligence into the mirror by

implementing a self-adjusting N-way tree allows a recursively fault tolerant solution.

The Figure illustrates the tree topology. The Figure shows the Data Source at the top left with a line drawn to its 'software RAID 1 mirror volume'. This volume, hosted on the Data Source, is the logical root of the N-way IP mirroring data redundancy tree, and is the initial target for new data. The local SCSI LUN shown is the mirror primary, and the iSCSI LUN - labeled 'iSCSI VLUN A' is the first branch of the tree. In the branches of the tree VLUN refers to 'Virtual LUN', since while the iSCSI target is exporting the address for 1 LUN, how that 'VLUN' maps to physical LUNs is up to that iSCSI device. In fact, the Figure depicts a mapping of iSCSI VLUN A to 2 other mirror volumes, shown with

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the 2 connection lines coming out of the iSCSI VLUN A box labeled 'VLUN A mapping'. Then those iSCSI VLUNs map to 2 other mirror vo...