Abstract
In this chapter, one of the truly outstanding features of Tru64 UNIX clustering: the Cluster File System (CFS) has been discussed. The CFS is conveniently sandwiched between the Virtual File System (VFS) and the physical file systems and acts as a router directing Input/Output (I/O) from the VFS to all parts physical. It's true that the CFS is a client-server implementation; however, the TruCluster engineers at Compaq are continually improving the CFS to reduce the amount of communication between CFS clients and the CFS servers. The command cfssmgr (8) is used to see which member is the CFS server for each file system or domain. Mounting a file system on only one member is pretty easy. The “-o server_only” option to the mount (8) command is added. There are several rules and regulations to partition a file system. The CFS Server tends to throw in a token as a free gift when sending I/O to a CFS client. Tokens are a lightweight synchronization method used by the CFS server to guarantee that every cluster member has the same view of a file; this is known as cache coherency. There are two token modes. Concurrent Direct I/O was introduced in V5.16 and enables members with direct access to the device where the file lives to bypass the CFS server for I/O not related to log updates and metadata operations like file size changes, etc. Although there is no automatic CFS server load-balancing facility, a CFS server relocation script can be used at system startup or within a CAA application resource action script 8 to automatically relocate file systems to specific members.
Published Version
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