In my efforts to get the hell away from RDM disks in VMware, using the Dell Compellent for iSCSI connections became a necessity.There’s good blog post here that runs through most of this. I’ve added some things from my own experience.
I use FC connections to the Dell for the VMware hosts so the iSCSI is solely for Windows clients and the Microsoft iSCSI Initiator.
The Compellent will need one iSCSI card installed in each storage controller, preferably on a 10Gb backbone. This article will not cover installing the cards or setting up the VLAN on the core switches, just what to do afterwards.
I’m using two iSCSI cards in the Compellent with Ethernet connections to stacked Cisco Nexus 7000 10Gb core switches. Each iSCSI card has two ports so there are four wire runs to the Nexus pair, one wire in each switch (port 1 in switch 1 and port 2 in switch 2).
How the Compellent Manages iSCSI Connections: Fault Domains
The array uses Fault Domains (FD) to manage multiple connections to its ISCSI card ports on either controller. Another way to put this is a FD is used to group physical ports together behind a logical IP. FDs are created at the Local Port configuration level on the array and can be assigned to each iSCSI card port. FDs sit in front of the port logically so assigning a FD to a port doesn’t eliminate the need for the port’s individual IP address.
The Windows iSCSI Initiator will use the FD IP and will not know about the individual IP addresses of the ports themselves. This is good because I didn’t want to configure multiple connections to each port in the Windows iSCSI Initiator.
A Fault Domain IP acts like a VIP with added design options: it can group ports on each controller and FDs can be on the same logical subnet. Consider this design with the iSCSI VLAN number being 37.
FD1 – 10.1.37.24 – Assigned to port 1 on physical iSCSI card 1 and 2
FD2- 10.1.37.25 – Assigned to port 2 on physical iSCSI card 1 and 2
This provides a mini-mesh design logically and a balanced design that complements Windows’ MPIO setup. It also gives a bit of business continuity since a logical FD is connected to physical ports on two controllers.
The ports themselves have IPs on the same VLAN.
Step 1- Setup the Fault Domains in the Compellent. Two IPs are needed.
In the Storage Management–>System–Setup–Configure Local Ports menu click the iSCSI tab. Click the Edit Fault Domains button then choose Create Fault Domain. In the General tab choose the name (make sure the Type is iSCSI). Click the IP Settings button and fill in the info needed (IP, Mask, Gateway, Port Number).
I created two Fault Domains. After creation they must be assigned to specific ports. Follow the same path listed above to open the Configure Local Ports menu. Assign one FD to each port on both iSCSI cards:
In the above design there is an iSCSI card in slot 1 of each storage controller (42,43) in the Compellent array. Each iSCSI card has two ports with a different FD assigned to each port on each card. the Purpose does need to be set to “Front End”.
Step 2- Assign IP addresses to the iSCSI card ports.
From Storage Management–>System–Setup–>Configure iSCSI IO Cards menu assign all the IP addresses:
This follows the same design aspect. All of the ports are in the iSCSI VLAN (37).
When finished this will be the logical setup:
FD1- 10.1.37.24 represents port 1 on each card (10.1.37.22 and 26)
FD2- 10.1.37.25 represents port 2 on each card (10.1.37.23 and 27)
Microsoft’s iSCSI Initiator will contact each FD for access unaware of the dual ports behind them.
All of this can be done on the fly after the iSCSI cards are installed in each controller. The installation of the cards will bounce each controller so plan accordingly.
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