Browse Prior Art Database

Maintaining Data Coherency in a Cluster of AIX Systems

IP.com Disclosure Number: IPCOM000112829D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Devarakonda, M: AUTHOR [+2]

Abstract

Disclosed is a coherency mechanism for an AIX*-based cluster file system. The cluster file system allows processes running on a cluster node to access files residing on the disks of any cluster node. This single-image functionality allows concurrent read-write sharing of file data within the cluster. The cluster file system caches file data in each cluster node to take advantage of locality of reference. Local caching coupled with concurrent sharing requires solving the problems of serialization of accesses to shared data and maintenance of cache consistency. To serialize accesses to shared files, the cluster file system uses a token-based locking scheme. This disclosure describes a scheme by which cache consistency is piggy-backed on the serialization mechanism.

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Maintaining Data Coherency in a Cluster of AIX Systems

      Disclosed is a coherency mechanism for an AIX*-based cluster
file system.  The cluster file system allows processes running on a
cluster node to access files residing on the disks of any cluster
node.  This single-image functionality allows concurrent read-write
sharing of file data within the cluster.  The cluster file system
caches file data in each cluster node to take advantage of locality
of reference.  Local caching coupled with concurrent sharing requires
solving the problems of serialization of accesses to shared data and
maintenance of cache consistency.  To serialize accesses to shared
files, the cluster file system uses a token-based locking scheme.
This disclosure describes a scheme by which cache consistency is
piggy-backed on the serialization mechanism.  Such a cache
consistency scheme simplifies programming effort, and offers
efficiency through reduced inter-node communication and delayed
write-back of file data modifications.

      The token-based locking scheme provides lock and unlock
primitives to serialize accesses to the shared files.  A lock can be
obtained in a read (shared) mode or in a write (exclusive) mode.  A
lock can be granted only if the node has a "token" for the file in
the required mode.  Therefore, when the first lock call is made for a
file, the cluster node must first obtain the token for the file in
the required mode.  (At any given time, multiple read tokens or a
single write token can be outstanding.)  The serialization protocol
requires a node to give up a token when another node needs it.  This
d...