an iSCSI question

This is some of the configuration rules for iSCSI and CLARiiON. Please see the Host Connectivity Guides for each operating system - there may be slightly different requirements.

You also need to take into consideration a condition called "Delayed ACK" - for Windows you need to make a registry change and this may be an issue for ESX and Solaris.

iSCSI Network connectivity

Dedicated storage networks are highly recommended, but not required. If not using dedicated storage networks, it is recommended that iSCSI traffic be either on separate physical LAN segments or on VLANs separate from those used for general LAN traffic. While VLAN tagging is not supported if received by a storage system¿s iSCSI ports, Ethernet switch-based VLANs are supported and can be useful in isolating iSCSI traffic from general LAN traffic.Servers can connect to a storage system using a Layer 2 (switched) or Layer 3 (routed) network.

Supported network switches and routers

Industry standard network switches and routers with 1-Gigabit copper connectivity to the storage system. If you want to use jumbo frames (that is, a maximum transmission unit of greater than 1500 bytes), all switches and/or routers in the paths to the storage system must support and be set up for the desired maximum transmission unit.

Number of servers and iSCSI storage systems

As many as available on the network, provided each server follows the following fan-in rule and each storage system follows the following fan-out rule.

iSCSI fan-in rule

A server can be networked to a maximum of 4 storage systems. A server can have a maximum of four NICs or HBAs (host bus adapters) connected to one storage system. A server cannot use both NICs and HBAs to connect to iSCSI storage systems; it must use either all NICs or all HBAs. Only one connection per initiator to each SP port is allowed.

When this document was released, AIX, HP-UX, and Solaris servers support only NIC connections to CLARiiON storage-system iSCSI data ports. For the latest supported AIX, HP-UX, and Solaris configurations refer to the E-Lab Interoperability Navigator or the AIX, HP-UX, or Solaris iSCSI Attach Release Notes on Powerlink.

Note: An initiator is any NIC or HBA port with a unique iSCSI name or ID in a server that has access to an SP. The AIX, HP-UX, Solaris, VMware ESX iSCSI initiator software and the Microsoft iSCSI Software Initiator assign the same iSCSI name to all NIC initiators in the server so they are seen as one single initiator.

A server can connect to both CLARiiON and Symmetrix iSCSI storage systems over a common network configuration if the server has common failover software and driver support for both storage-system types.

iSCSI fan-out rule

The Navisphere software license determines the number of iSCSI servers you can connect to a CX4-120, CX4-240, CX4-480, CX4-960, CX3-10c, CX3-20c, CX3-40c, CX300i, or CX500i storage system. The software installed on an AX4-5i or AX4-5SCi storage system determines the number of iSCSI servers that you can connect to the storage system. The maximum number of connections between servers and a storage system is limited by the number of initiator records supported per storage-system SP. An initiator is a NIC or iSCSI HBA port in a that can access a storage system. Note that some NICs or iSCSI HBAs may have multiple ports. Each NIC or iSCSI HBA port with a connection to an SP port is one path to that SP and the storage system containing that SP. Each path consumes one initiator record. Depending on the type of storage system and the connections between its SPs and the network, a NIC or iSCSI HBA port can be connected through different router or switch ports to the same SP port or to different SP ports, resulting in multiple paths between the NIC and the iSCSI HBA port and an SP and/or the storage system. Note that the failover software environment on the server may limit the number of paths supported from the server to a single storage-system SP and from a server to the storage system.

Number of servers

Note: Highly-available (HA) servers are ones with an equal number of connections to each SP in the storage system.

For CX4-120 - up to 128 HA servers
For CX4-240 or CX4-480 - up to 256 HA servers
For CX4- 960 - up to 512 HA servers
For CX3-10c, CX3-20c, CX3-20f, CX3-40c, CX300i, or CX500i

iSCSI connection speed

By default, CX4-120, CX4-240, CX4-480, CX4-960, CX3-10c, CX3-20c, CX3-40c, AX4-5SCi, or AX4-5i storage system auto-negotiate the connection speed of their iSCSI ports. You can force a fixed connection speed of 10, 100, or 1000 Megabits/sec using either Navisphere Manager or Navisphere CLI.

The CX300i and CX500i iSCSI ports operate at 1-Gigabit/sec so any network devices, NICs, or HBAs ports connected to them must operate at 1-Gigabit/sec.

kelleg, thanks very much for the info, it's very informative, however, i still have this question, let me try to use an example, say i have 2 FE iSCSI ports connected to 2 physically different switches, and on the host side, 2 NIC's connected to the 2 switches as well, now do i configure the 2 iSCSI ports?

with 2 different networks such as 192.168.1/24 and 192.168.2/24, or put both iSCSI ports on the same network say 192.168.1/24? the reason i ask that question is that i think it's significant in terms of how the initiator(the host) would implement the failover, or maybe not, but that's what i'm trying to find out

ayh, so the iSCSI failover part partially resides on the OS's IP multipathing of the NIC cards, rather than entirely on the SAN-related software's(EMC PowerPath or Veritas's DMP) multipathing capability, unlike Fiber Channel traffic, very interesting...thanks kelleg!

Be careful with Windows - you can bypass Windows MPIO by ensuring that when you setup the iSCSI connections (Discovery and Log on) if you specifically select the Source IP address of the NICs on the host. Go to the Advanced settings when you log on and look at the three drop downs - the middle one has the Source IP - be sure to select this one. When you take the "default" , Windows will pick the NIC to use - this could be the LAN NIC if you're not careful.

glen

Thanks Glen!