Messages in this thread | | | Date | Sat, 15 May 1999 21:31:24 -0400 (EDT) | From | "Albert D. Cahalan" <> | Subject | Re: Linux & NFS caching: reducing TCO |
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Charles K Hardin writes:
> Excerpts from RFC 1094 - Network File System ver 2 ... > In no uncertain terms does NFSv2 Spec allow server-side caching, just > because implementations do this - does not make it conform to a spec.
Eh, so what?
Both server and client need caching options, with the defaults being some kind of compromise.
> since there are no callbacks in NFS (ie, no way to invalidate a cached > file on the client). This is the price you pay for stateless servers in ... > hack to get a choerence protocol running between the clients).
BSD's NQNFS ("not quite NFS") protocol supports this. http://www.netapp.com/technology/level3/nfsbook.html
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The NFS implementation that appears in 4.4BSD was written by Rick Macklem at the University of Guelph using the specifications of the Version 2 protocol published by Sun Microsystems [Sun Microsystems, 1989; Macklem, 1991]. This NFS Version 2 implementation had several 4.4BSD-only extensions added to it; the extended version became known as the Not Quite NFS (NQNFS) protocol [Macklem, 1994a]. This protocol provides
* Sixty-four bit file offsets and sizes
* An access RPC that provides server permission checking on file open, rather than having the client guess whether the server will allow access
* An append option on the write RPC
* Extended file attributes to support 4.4BSD filesystem functionality more fully
* A variant of short-term leases with delayed-write client caching that give distributed cache consistency and improved performance [Gray & Cheriton, 1989]
Many of the NQNFS extensions were incorporated into the revised NFS Version 3 specification [Sun Microsystems, 1993; Pawlowski et al, 1994]. Others, such as leases, are still available only with NQNFS. The NFS implementation distributed in 4.4BSD supports clients and servers running the NFS Version 2, NFS Version 3, or NQNFS protocol [Macklem, 1994b]. The NQNFS protocol is described in Section 9.3.
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At the same place (http://www.netapp.com/technology/level3/nfsbook.html) you can find some information about how leases work.
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