3.4.0 Matrix Server Release Notes

PolyServe Matrix Server Release Notes 7

Filesystem Semantics

The PSFS filesystem differs semantically from the NTFS filesystem in the

following ways:

• A file cannot be deleted if it is currently open on another node.

• A file cannot be “renamed over” if it is currently open on another

node. For example, an attempt to rename filea to fileb will fail if fileb is

currently open on another node.

• The time that a file was last accessed is not updated after a successful

read operation, even on the local node.

• When a directory is renamed, subsequent change notify requests

within that directory are not completed. For example, if Windows

Explorer is open at a certain directory on the local node and that

directory is renamed on a remote node, any subsequent changes to the

renamed directory will not appear in the local Explorer window. You

will need to close and reopen Explorer to see the renamed directory.

• Memory-mapped files are not coherent across nodes. Because PSFS is

a shared filesystem, the same file can be mapped into memory on

more than one node. When a change is made to a file on a remote

node, the local node does not see the change immediately. This occurs

because the operating system on the remote node may not

immediately write the change to disk. Consequently, PSFS allows

writes to files that are being executed on other nodes.

• If the Bypass Traverse Checking privilege is not enabled, differences in

traverse access checking for Directory Change Notification (DCN)

may be observed. On NTFS, before a change notify request is

completed, an access check is performed to determine whether the

subscriber has traverse access to the directory in which the contents

were modified. If the subscriber does not have traverse access, the

change notification will not be delivered.

On PSFS, this check is not performed and the contents of directories

(e.g., the names of files) may be exposed via DCN to a user who would

otherwise not obtain this data. Traverse access checking other than

during directory change notification is as expected, so access to file

contents is not compromised. The user is advised not to depend on