CIFS vs. NFS and other filesystems (was Client for Samba Networks)

[Steven French]

>Subject: Re: Client for Samba Networks

>On Mon, Dec 17, 2001 at 01:31:10PM -0600, Christopher R. Hertel wrote:

>> SMB is icky, NetWare is even more closed, and NFS is okay, but somewhat
>> outdated.  Coda has lots of problems, but one thing it has in its favor
>> is disconnected operation.

> Tim Potter wrote:
>Have a look at nfs v4.  It's very nice both compared to SMB and previous
>versions of nfs.

Sounds like we are overdue for a high level comparison of network
filesystems.   Here are some
initial observations:

CIFS:
     Strengths:
     a) Huge installed client base (not just Windows),
     b) good, open source server implementation available (Samba!),
     c) token management (oplock) and referral ("dfs") semantics are a good
compromise between usefulness and simplicity
     d) the key part of the filesystem protocol (mostly) documented,
     rich file open semantics map well to Windows and related OSs,
     e) kerberos security integration and RPC integration
     f) broader in scope (print, ACL, browsing etc.) than other filesystem
protocols
     g) optional PDU signing above the RPC allowing maximal flexibility
     h) Unicode
     i) high performance
     j) huge amount of loosely related management/administrative function
available via various DCE RPC calls
     k) efficient PDUs (small frame headers, less wasted bandwidth)

     Weaknesses:
     a) the extended protocol poorly documented,
     b) not an IETF standard
     c) elements of older protocol dialects still needed adding to
complexity of implementations
     d) protocol needs addition of lock migration/recovery and support for
new transport mechanisms (e.g. RDMA)
     e) ACL support - although useful is hard to understand
     f) (item j above) management/admistrative calls are proprietary

NFSv3:
     Strengths:
     a) relatively simple to implement
     b) maps well to Unix VFS semantics (except for caching)
     c) protocol easy to understand by stripping file protocol to its
minimum
     d) Unicode

     Weaknesses:
     a) statelessness of core protocol causes caching problems
     b) few Windows NFS clients installed
     c) maps poorly to Windows operating system API
     d) poor security (forcing it into lower layers if at all)
     e) not a standard (informational description published by Sun as
informational RFC)
     f) relatively weak open source server implementation (at least
compared to Samba and AFS) has scalability problems
     g) implementing many protocols needed to get CIFS equivalent e.g. lock
manager, mount and port mapping protocol, SunRPC, NIS, ONC extensions (some
proprietary)
     h) WebNFS enhancements partially implemented adding to some confusion


NFSv4:
     Strengths:
     a) on track to be an IETF standard
     b) improved recovery (lock migration)
     c) supports Windows file sharing semantics better than NFS v3 did
     d) safe file caching

     Weaknesses:
     a) few clients
     b) perceived lack of Microsoft interest
     c) the existing prototype open source implementation is tricky to
integrate into current Linux kernels
     d) protocol is moving target (it is not quite done yet)
     e) too late?
     f) complex

DAFS:
     Strengths:
     a) Addition of RDMA to NFS style protocol, (probable) high performance
in clusters and server farms.
     b) (see NFS v4)

     Weaknesses:
     a) unproven, lack of client support, perceived competition with NFS v4
     b) (see NFS v4)

HTTP/WebDAV
     Strengths:
     a) official standard
     b) broadly implemented
     c) well suited to internet
     d) active standardization work - protocol will improve

     Weaknesses:
     a) frame headers are large (high % of frame size is wasted)
     b) security integration not optimal
     c) slow
     d) not a complete match to either Linux VFS or Win2K IFS API
requirements

NCP(Netware):
     Strengths:
     a) NDS integration
     b) good match for Windows
     c) good installed base on older systems

     Weaknesses:
     a) Proprietary
     b) poorly documented
     c) not a standard
     d) complex, with lots of dialects
     e) future clients questionable


AFS/DFS:
     Strengths:
     a) sophisticated distributed caching (token management)
     b) DCE integration (including Kerberos and RPC)
     c) standardized by OpenGroup

     Weakness:
     a) lack of clients
     b) bulky, slow Windows clients
     c) server integration with Unix operating systems and server
filesystem is complicated
     d) most implementations were expensive
     e) complex to implement


Coda:
     Strengths:
     a) disconnected support

     Weaknesses:
     a) Lack of commercial implementations
     b) lack of Windows clients
     c) not well understood

Comments?

Steve French
Senior Software Engineer
Linux Technology Center - IBM Austin
phone: 512-838-2294
email: sfrench at us.ibm.com