Editing Single system image (section)

===Single root===
Most SSI systems provide a single view of the file system. This may be achieved by a simple [[Network File System (protocol)|NFS]] server, shared disk devices or even file replication.

The advantage of a single root view is that processes may be run on any available node and access needed files with no special precautions.  If the cluster implements process migration a single root view enables direct accesses to the files from the node where the process is currently running.

Some SSI systems provide a way of "breaking the illusion", having some node-specific files even in a single root. [[Hewlett-Packard|HP]] [[TruCluster]] provides a "context dependent symbolic link" (CDSL) which points to different files depending on the node that accesses it.  [[Hewlett-Packard|HP]] [[VMScluster]] provides a search list logical name with node specific files occluding cluster shared files where necessary. This capability may be necessary to deal with ''heterogeneous'' clusters, where not all nodes have the same configuration. In more complex configurations such as multiple nodes of multiple architectures over multiple sites, several local disks may combine to form the logical single root.