VERITAS Storage Foundation 4.1 Cluster File System HP Serviceguard Storage Management Suite Extracts, December 2005

Appendix ,
VxFS Functionality on Cluster File Systems
3
CFS and the Group Lock Manager
CFS uses the VERITAS Group Lock Manager (GLM) to reproduce UNIX single-host file
system semantics in clusters. This is most important in write behavior. UNIX file systems
make writes appear to be atomic. This means that when an application writes a stream of
data to a file, any subsequent application that reads from the same area of the file will
retrieve the new data, even if it has been cached by the file system and not yet written to
disk. Applications can never retrieve stale data, or partial results from a previous write.
To reproduce single-host write semantics, system caches must be kept coherent and each
must instantly reflect any updates to cached data, no matter from which cluster node they
originate. GLM locks a file so that no other node in the cluster can update it
simultaneously, or read it before the update is complete.
VxFS Functionality on Cluster File Systems
The VERITAS Cluster File System is based on the VERITAS File System (VxFS). Most of
the major features of VxFS local file systems are available on cluster file systems,
including:
◆ Extent based space management that maps files up to a terabyte in size.
◆ Fast recovery from system crashes using the intent log to track recent file system
metadata updates.
◆ Online administration that allows file systems to be extended and defragmented
while they are in use.
The following is a list of features and commands that operate on CFS. Every VxFS online
manual page has a section on Cluster File System Issues with information on whether the
command functions on a cluster-mounted file system and indicates any difference in
behavior from local mounted file systems. You can also review the VERITAS Storage
Foundation Cluster File System Release Notes for information on the latest CFS features.