A distributed lock manager (DLM) provides distributed applications with a means to synchronize their accesses to shared resources.
Clusters
Combining two or more computers into a cluster in which the machines can use each other's hard disks via a unified file system offers significant advantages for performance and availability. DLMs have been used as the foundation for clustered file systems with considerable success by using cluster wide locks not only for file locking but also for coordination of all disk access. VMScluster, the first clustering system to come into widespread use, relied on the OpenVMS DLM in just this way.
Red Hat and Oracle have both developed clustering software for Linux. Both projects include a DLM modelled on the venerable VMS DLM. (OCFS2, the Oracle Cluster File System[1] has been included[2] in version 2.6.16 of the official Linux kernel. Red Hat's cluster software[3], including their DLM[4] is available as a kernel patch.)
SSI Systems
A DLM is also a key component of more ambitious single system image projects such as OpenSSI.