Editing OpenSSI (section)

====CFS====
CFS, the OpenSSI Cluster File System provides transparent inter-node access to an underlying ''real'' file system on one node.

CFS is ''stacked'' on top of the real file system and co-ordinates access from different nodes using a ''token'' mechanism.  One node has physical access to the underlying file system and performs all read and write operations.  At any one time one node ''owns'' a token, representing a part of the underlying file, this implies that that part of the file is in the cache of the owning node.  If another node tries to access that part of the file the token is ''stolen'' and the cache contents are copied to the stealing node.  The OpenSSI CFS implementation is remarkably similar to that used by [[Hewlett-Packard|HP]] [[TruCluster]].<ref>
{{Citation
 |title = TruCluster Server Handbook
 |first1 = Scott
 |last1 = Fafrak
 |first2 = Jim A.
 |last2 = Lola
 |first3 = Brad
 |last3 = Nichols
 |first4 = Gregory
 |last4 = Yates
 |pages = 342–345
 |publisher = Digital Press
 |isbn = 1-55558-259-1
 |year = 2003
}}
</ref>

CFS is also used to co-ordinate access to shared memory segments.

CFS can be used in a fault tolerant system by using shared disk subsystems (dual ported [[SCSI]] or [[Storage area network|SAN]]), or by using [[DRBD]].  If the node that is currently directly accessing the file system crashes then the CFS mount ''fails over'' to the other node that is directly connected to the disk and the cluster now accesses the file system via that node.