Problem: Clients using nfs (Sun and HP unix workstations) were taking much longer to open files. Home, Tools, and Project data was moved to the filer and it was running GigE To open a drawing, it took 2hrs vs 20min on a older Sun server running 100mb ethernet. Data OnTap v6.1.2R1

Once we made changes, it now takes 18min to open the same drawing (this is a normal time for the types of schmetics they are working on).

Solution (so far): Use options nfs.udp.xfersize 8192 (instead of the default 32768) Also, set the filer to match the cisco switch for flow control (cisco has send flow, filer now has receive)

ToDo: Investigation to see if full flow control will improve performance even more. Try enabling TCP over nfs Make sure that the xfersize does not serously affect the few machines we have on GigE that mount from the filer

Thanks to the following for all the help and email (hope I didn't forget anyone).

Philip Meidell John F. Detke Paul Jones Neil Stichbury Mike Ball Adam Fox Neil Stichbury devnull@adc.idt.com (whoever your are :-)

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The major known issue is with NFS over UDP and packet drops causing the UDP cascading error problem. If you are running NFS over UDP I'd strongly suggest switching to NFS over TCP.

I believe this is a buffering issue, where the Gig interface is "overloading" a buffer somewhere on its way to a 100M interface, and packets gets dropped. When that happens the entire UDP datagram gets resent. Also check rsize/wsize on the client, it may work better set to 8k, rather than the (default?) 32KB.

This problem is related to network hardware, I've seen in most often on Cisco gear but it happens with others too. A quick nfsstat on client(s) can show the problem, look for retrans stats.

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We had a similar problem and solved it by changing the UDP transfer size. Have a look at bug ID 29146 which includes the following :-

"In Data ONTAP 5.3.4 and earlier releases the default UDP transfer size is

8192. In 5.3.5 and later releases the default is 32768. This larger value

improves performance in some situations, but may cause problems in others.

Problem 1 - 100-Mbit client is reading from Gigabit interface With the larger default, problems may result when the Gigabit interface on the filer is sending to a 100-Mbit client. Switches can drop packets on the outbound 100-Mbit port because too many packets become queued due to the difference in line speeds and the larger transfer size. Few complete 32K UDP datagrams are received by the

client, and the client assumes the filer has gone away and increases its delay between retries. Poor performance may be seen. If a client does not specify the rsize and wsize parameters in the mount command, the filer's default UDP transfer size is used. If a client does specify rsize and wsize, and the values are larger than the default, then the default is used. This means that you may see problems after you upgrade from 5.3.4 (or earlier release) to 5.3.5 (or later release) if the resulting transfer size is 32768. Problem 2 - Multiple

clients are reading from 100-Mbit interface When the UDP transfer size is 32768 and multiple clients are reading from a 100-Mbit interface, the driver transmit queue on the filer can overflow more readily and packets may be discarded. This can lead to erratic or poor performance on the clients."

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First thing to check in GigE is typically flow control settings on the switch, filer, and client side. Typically it's best to have both transmit and receive flow control turned on. On the filer, it's called full flowcontrol. That isn't the default for some switch vendors and OS NICs.

It's at least a start. Like most performance issues, you may have to work several rounds of stuff to find the culprit. Before you open a case with NTAP, which I strongly suggest, you may need to quantify your performance in some way. MB/sec is a good one. By putting a value on your performance it's easier to figure out what areas could be wrong and also easier to figure out when you can't get anymore based on your environment. That's the thing with Gigabit, most clients can't max it out so you will hit a ceiling for a single client that is less than the capacity of the wire. Slower forms of Ethernet were easier in this way because you knew pretty much where the ceiling was.

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now that you have mentioned running Sun boxes try this in the /etc/system file of one of them and see if you perceive a performance improvement.

set sq_max_size=2048 set nstrpush = 90 set nfs:nfs3_max_threads = 24 set nfs:nfs3_nra = 10 set nfs:nfs_max_threads = 24 set nfs:nfs_nra = 10

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When you're using NFS over UDP with disparate speeds, i.e. gigabit to the switch, then fast ethernet to clients, you can address performance problems in one of two ways:

1. If all of your client machines are on fast ethernet (yep, that means NO

gigabit clients) the simple approach is to set the filer option

options nfs.udp.xfersize 8192

If you do have gigabit clients, doing the above will impact performance to them, in which case you have to do the more management intensive step two...

2. If you have some gigabit client machines, add the following options to

the mount command on each 100 Mbit client machine: wsize=8192,rsize=8192