iSCSI Question, why 2 connections?

[QantasA380]

HI,

Sorry for the really daft question. All of our our ESXi hosts have 2 connections to the HP StorageWorks iSCSI device. Why does each server have 2 connections please? Why not 1? Is it for redundancy?

Many Thanks

[a_p_]

Redundancy is usually the main reason for this setup. In addition to redundancy - depending on the setup and the storage capabilities - you can also improve throughput using multiple connections.

André

[QantasA380]

Thanks, im not after changing it, just want a better understanding :smileyhappy:

[a_p_]

For a better understanding of this part of the setup, try to get a hold on the storage vendor's recommendation for setting up ESX(i). Most storage vendors offer a best practice guide for securing and optimizing access to their different storage systems.

André

[Andy_Banta]

> Thanks, im not after changing it, just want a better understanding.

There would be a few answers to this question, depending on your configuration.

If you simply enabled SW iSCSI on your host, and are using something like a 2000i G2, the reason for the two connections is that when you discover the device, it responds with infomration about how to connect through both ports.  ESX starts connections based on each of the discovered devices.

If you look at your iSCSI configuration, you probably added a single dynamic discovery address.  If you look at the "static discovery" tab, you'll see the two targets or portals that were discovered, and ESX has established a session to each.

Alternatively, if you were using an HP Lefthand box and had configured ESX to use two physical NICs for iSCSI (as described in chapter 2 os the iSCSI SAN Config Guide: http://www.vmware.com/pdf/vsphere4/r41/vsp_41_iscsi_san_cfg.pdf ), you would end up with two connections because each port on the ESX host would be seen as a storage end-point.

You can do the same ESX setup when connecting to 2000i, and in that case, you'll end up with 4 paths and no single point of failure on the host side, as well.

There's more useful information on iSCSI setup in

http://virtualgeek.typepad.com/virtual_geek/2009/09/a-multivendor-post-on-using-iscsi-with-vmware-vsphere.html

Enjoy,

Andy