Jumbo Packets

In the past few months, we’ve gradually been implementing a new SAN solution from Dell that uses iSCSI. We are kind of learning as we go and there are always bumps in the road. I’d noticed we had some I/O issues on our main production SQL Server but nothing seemed to add up and I couldn’t find where the problem could be outside of tuning indexes or putting data files on a different drive. We are on SQL Server 2000 but we are moving towards 2005 and I’m sure that might have helped me troubleshoot the problem. I came across something the other day about Jumbo packets. As I read more and figured out where to check things I figured out I might have been onto something. Brent Ozar passed me this link that helps check on the packet size. I looked at the iSCSI connection(NIC card –> Configure –> Advanced) and noticed that the Jumbo Mtu was set to 1500. I asked more questions of our admin and everything else along the pipe had been raised to 9000, but somehow the card got missed. Once I set this to 9000 I saw that I had far fewer I/O problems. They are still there due to poor indexes and disk contention but they are better than they were. Just thought I’d pass this along in case anyone else had a similar issue with iSCSI.

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