i know the option ip.tcp.sack.enable should be turned off in some case at least it should be considered as a way to correct some perf problems SACK was/is not trully tested and achived and I saw windoz'sack trying to speak w/ netapp's sack w/ lot of problems : lost connection, no way to copy files and so... we encounter this prb between a netapp in 64X and all XP (but not w/ 2K) put the window size back to what it was before doing this try
Brubaker, Paul wrote:
We're experiencing severe latency when a Windows 2000pro or Windows XP client reads and writes to a folder on our Netapps (FAS960 w/ Data Ontap 6.5.1). It only seems to be client O/S as our testing w/ a Windows 2000 Server did not have latency on reads / writes.
We're currently looking at SACK and TCP Window sizes. Has anyone experienced severe client latency? Any know issues / advice? Anyone changing the sack option on their Filers?
Thanks!
Related info below:
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SackOpts
This parameter controls whether or not SACK (Selective Acknowledgement) support is enabled, as specified in RFC 2018. SACK is especially important for connections using large TCP Window sizes.
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
SackOpts="1" (DWORD - boolean, recommended setting is 1. Possible settings are 0 - No Sack options or 1 - Sack Option enabled).
_http://www.speedguide.net/read_articles.php?id=157_
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One more item of note. In the traces from the slow xp box, we're showing a boatload of SACK transmissions, whereas in the fast one, not a one. I'd like to turn off SACK on the filer side to see if things clear up or not as google isn't giving me much luck in the 'which registry entry do I change to check things on the windows box' angle.
On the filer:
filer> options ip.tcp.sack.enable off
Paul M. Brubaker, Jr. RIDS - Intel System Support AT&T Wireless - Harrisburg PA e-mail: paul.brubaker@attws.com office #: 717-526-5011 cell #: 717-578-2254