iSCSI storage networking: What you need to know

As simple as iSCSI is to get running, configuring it to perform optimally requires a solid knowledge of how it actually works

Over the past two weeks, I've written about some of the commonly overlooked aspects of building a bulletproof IP storage network and how to best use that network with NFS. This week, I'll show you the ins and outs of configuring iSCSI for performance and redundancy, as well as how it compares with NFS.

The first thing to understand is that although NFS and iSCSI are both IP storage protocols supported by many server operating systems and hypervisors, that's about as far as the similarity between the two extends. NFS is a high-performance file-sharing protocol in the same vein as SMB/CIFS, while iSCSI is a block-level storage protocol more akin to Fibre Channel in that it encapsulates raw SCSI commands. This distinction is important because it has significant bearing on how you get redundancy and performance scalability.

iSCSI vs. NFS on the network: How they differ

When comparing the networking requirements of NFS and iSCSI, the largest practical difference is that the iSCSI protocol has built-in redundancy and link aggregation capabilities, called multipath input/output (MPIO). NFS lacks MPIO. You can use MPIO to offer both link redundancy and additional throughput -- entirely without the use of the problematic NIC/link teaming that's required to do the same for NFS.

In a typical NFS configuration, servers are each configured with a single-storage IP address bound to a NIC team spread across two stacked switches. On the storage side, the same configuration is duplicated, except that the storage is generally configured with a second IP address alias to allow better load balancing over the team members because the NIC teaming algorithms use source and destination IP address to load-balance traffic. In this scenario, the failure of an individual link or entire switch stack member is handled by the NIC teaming software -- the NFS client and server software isn't involved.

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