Unless you've been living under a rock for the last five years, you've probably heard about iSCSI, a transport protocol for sending SCSI commands over an IP network. As a networking value-added reseller (VAR), there's
At the heart of every iSCSI SAN is an IP network. At the very least, you should set up a gigabit Ethernet switched network using CAT 5E or 6 cabling. If possible, set all the ports on the switch(es) to full duplex; no autonegotiation here. If left up to the clients and switches to decide the duplex mode, they may negotiate a setting that is less than optimal. Also configure all of the HBA and network adapters (initiators) that will be connecting to the SAN to use full duplex.
On a standard Ethernet network the frame size is 1,500 bytes. By turning on jumbo frames the frame size is increased to 9,000 bytes. Your customers running Windows will see a performance increase since the default block size for the NTFS file system is 8,192 bytes. Notice how that fits nicely into a jumbo frame? There's also plenty of room remaining for the headers and other overhead associated with Ethernet.
A network with lots of traffic can get bogged down when continually resending data that was lost in transit. Implement flow control on every switch port that will be handling iSCSI traffic. You should also make this setting on the initiators that will be connecting to the SAN. Earlier I mentioned that you should enable jumbo frames. Not all switches can handle both jumbo frames and flow control simultaneously. If forced to pick between the two, choose flow control.
Provision a separate network for iSCSI traffic to segregate the iSCSI traffic away from normal LAN traffic. You want to do this because iSCSI traffic is unicast traffic and can typically utilize the entire link. If the switch(es), by default, have unicast storm control enabled, you should disable it. If a separate network is simply out of the question then, at the very least, configure a separate VLAN for the iSCSI traffic.
Remember that the SAN relies on the network to be there at all times, 24 hours a day, seven days a week. So, if a switch decides to go out to lunch, the SAN will most likely suffer a fairly significant failure. The last thing you want is a customer calling you in the middle of the night because you didn't build some redundancy into the network.
If you hadn't considered these five important points about IP networked (iSCSI) storage, I hope this article was able to enlighten you a bit. The more you know about the intricacies of IP network storage, the sooner you can begin helping your customers get started with their first iSCSI SAN.
About the author
David L. Stevens has been working in the information technology field for more than 15 years. During that time he has held a series of progressively responsible IT positions in both higher education and corporate sectors. He is the Storage Manager for Carnegie Mellon University where he is responsible for the institution's iSCSI storage area networks and backup services.
This was first published in May 2007