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diff --git a/share/FAQ/NFS.FAQ b/share/FAQ/NFS.FAQ deleted file mode 100644 index e6f7af8..0000000 --- a/share/FAQ/NFS.FAQ +++ /dev/null @@ -1,77 +0,0 @@ -FreeBSD and NFS [for a FAQ] - -Certain Ethernet adapters for ISA PC systems have limitations which -can lead to serious network problems, particularly with NFS. This -difficulty is not specific to FreeBSD, but FreeBSD systems are affected -by it. - -The problem nearly always occurs when (FreeBSD) PC systems are networked -with high-performance workstations, such as those made by Silicon Graphics, -Inc., and Sun Microsystems, Inc. The NFS mount will work fine, and some -operations may succeed, but suddenly the server will seem to become -unresponsive to the client, even though requests to and from other systems -continue to be processed. This happens to the client system, whether the -client is the FreeBSD system or the workstation. On many systems, there is -no way to shut down the client gracefully once this problem has manifested -itself. The only solution is often to reset the client, because the NFS -situation cannot be resolved. - -Though the "correct" solution is to get a higher performance and capacity -Ethernet adapter for the FreeBSD system, there is a simple workaround that -will allow satisfactory operation. If the FreeBSD system is the SERVER, -include the option "wsize=1024" on the mount from the client. If the -FreeBSD system is the CLIENT, then mount the NFS file system with the -option "rsize=1024". These options may be specified using the fourth -field of the fstab entry on the client for automatic mounts, or by using -the "-o" parameter of the mount command for manual mounts. - -In the following examples, "fastws" is the host (interface) name of a -high-performance workstation, and "freebox" is the host (interface) name of -a FreeBSD system with a lower-performance Ethernet adapter. Also, -"/sharedfs" will be the exported NFS filesystem (see "man exports"), and -"/project" will be the mount point on the client for the exported file -system. In all cases, note that additional options, such as "hard" or -"soft" and "bg" may be desireable in your application. - -Examples for the FreeBSD system ("freebox") as the client: - in /etc/fstab on freebox: -fastws:/sharedfs /project nfs rw,rsize=1024 0 0 - as a manual mount command on freebox: -mount -t nfs -o rsize=1024 fastws:/sharedfs /project - -Examples for the FreeBSD system as the server: - in /etc/fstab on fastws: -freebox:/sharedfs /project nfs rw,wsize=1024 0 0 - as a manual mount command on fastws: -mount -t nfs -o wsize=1024 freebox:/sharedfs /project - -Nearly any 16-bit Ethernet adapter will allow operation without the above -restrictions on the read or write size. - -For anyone who cares, here is what happens when the failure occurs, which -also explains why it is unrecoverable. NFS typically works with a "block" -size of 8k (though it may do fragments of smaller sizes). Since the maximum -Ethernet packet is around 1500 bytes, the NFS "block" gets split into -multiple Ethernet packets, even though it is still a single unit to the -upper-level code, and must be received, assembled, and ACKNOWLEDGED as a -unit. The high-performance workstations can pump out the packets which -comprise the NFS unit one right after the other, just as close together as -the standard allows. On the smaller, lower capacity cards, the later -packets overrun the earlier packets of the same unit before they can be -transferred to the host and the unit as a whole cannot be reconstructed or -acknowledged. As a result, the workstation will time out and try again, -but it will try again with the entire 8K unit, and the process will be -repeated, ad infinitum. - -By keeping the unit size below the Ethernet packet size limitation, we -ensure that any complete Ethernet packet received can be acknowledged -individually, avoiding the deadlock situation. - -Overruns may still occur when a high-performance workstations is slamming -data out to a PC system, but with the better cards, such overruns are -not guarranteed on NFS "units". When an overrun occurs, the units affected -will be retransmitted, and there will be a fair chance that they will be -received, assembled, and acknowledged. --- - John Lind, Starfire Consulting Services -E-mail: john@starfire.MN.ORG USnail: PO Box 17247, Mpls MN 55417 |
