We would be remiss in our descriptions of remote access file systems were we to omit mention of CIFS, which is used in Windows systems for remote file access.
CIFS is an improved version of Microsoft’s SMB (Server Message Block); proposed by Microsoft, CIFS was offered to the IETF (Internet Engineering Task Force) for adoption as a standard.
CIFS, installed on a PC, allows that PC access to data held on UNIX systems.
There is an important difference between NFS and CIFS. NFS is stateless, while CIFS is stateful.
This means that an NFS server does not need to maintain any state information on its clients, but a CIFS server must. Thus, in the event of a failure in either the network or the server, recovery is much more complex for a CIFS server than for an NFS server. NLM (Network Lock Manager) was provided to implement lock operations in NFS, but its use is not widespread. Version 4 of NFS supports locking.
Examples of products implementing CIFS include:
» Samba (free software);
» ASU (Advanced Server UNIX) from AT&T
» TAS (TotalNET Advanced Server) from Syntax
UNIX file systems need extensions to support Windows file semantics; for example, the “creation date” information needed by Windows and CIFS must be kept in a UNIX file system in a complementary file.
This diagram follows our practice of omitting some components for simplicity. We do not show the TLI (Transport Layer Interface) nor the NDIS (Network Driver Interface Layer), for example, nor do we show local accesses on the server. NTFS (NT File System) is the Windows 2000 native file system.
The I/O manager determines whether an access is local or remote; the request is either directed to the local file system or handled by the CIFS Redirector. This checks to see whether the data is available in the local cache and, if not, passes the request on to the network layers for forwarding to the server holding the file involved.
Source of Information : Elsevier Server Architectures
Saturday, 2 June 2012
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