Speed Mismatch?!?
- From: mschunk@xxxxxxxxxxxx
- Date: 7 May 2006 16:43:21 -0700
I've been banging my head on this one for weeks.
Can someone help me understand why network performance between Windows
2k/xp/2k3 hosts with a gigabit interface, and those with a 100/full
interface are slow so?
Now, 100/full to 100/full transfers are plenty fast. Very. And 1000
to 1000 transfers outright smoke...as gigabit should.
But, for large TCP transfers from a 1gbit host to a 100mbit host it
goes very Slow...
1) No matter what NIC used. Intel, Broadcom, D-Link, 3COM....or driver
version.
2) No matter what version of windows to other version of windows...or
different motherboards, etc...the slowness is very predictable no
matter what hardware involved.
3) No matter what type of gigabit switch....Cisco 3750, several
Netgears, some managed others not.
4) No matter how the switches involved are used...host and server in
same switch, slow. Host and server in different switches...linked
straight...routed between them...I even tried trunks between switches
together w/ link ag....always slow. Always the same.
5) No matter how many times I try different Ethernet cables...Cat5, 5e,
6...some pre-made, others made by hand.
6) No matter what TCP window sizes are set to anywhere, be it client or
server side or both.
I put gbit adapters in the servers, thinking they could use them to
sever files to all the workstations that have 100mbit NIC's. I mean,
it was logical...a gbit server "should" be able to handle 10x the
throughput to 100mbit clients, right???? Nope.
Note again that the performance problem is only one way. When I push
files FROM the 100mbit hosts, to the 1gbit servers, speed is expected:
fast, about 80mbit/sec. When I pull files form the 1bitg servers, to
the 100mbit PC's...speed is absolutely terrible. I'm taking
5mbit/sec, if that.
Looking at the packets...I'm seeing gobs and gobs of TCP retransmit
frames. It's like the switches (even the fancy Cisco one) are
sending data to the PC's faster than the PC's can take it....but
only when moving data from 1gbit to 100mbit. (So much for "store and
forward" switching.)
Also, in addition to the TCP re-Trans frames, the Cisco switch (when I
put in the patch between these hosts) is telling me I've got "late
collisions" on the gbit interface during the slow transfers. WTF?
The PC's are all 100/full, in auto. Everything is full duplex, so
why am I seeing ANY collisions of any kind at all???
Duplex mismatch, sure, I've dealt with that nastiness before, and I
think I understand how that messes things up....but I've NEVER heard
of a SPEED mismatch on Ethernet. Have You?
I'm coming to the conclusion that if I want to have gbit NICs around,
AND use them at that speed...I have to dedicate a totally separate
fabric for them. Great...so all my servers can talk to one another at
1000...at least backups will still smoke...but they must all serve at
the same speed as clients? Why did I even bother buying any gbit
switches if I can't really use them?
Help? What else can I try?
.
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