iSCSI and SAN storage

Using iSCSI for virtual machine storage has long been the regular thing to do. Even if you take into account the fact that iSCSI isn't the most efficient way to approach storage, it's still so widely accepted that you'll find it everywhere. Efficiency is compromised for two reasons:

• iSCSI encapsulates SCSI commands into regular IP packages, which means segmentation and overhead as IP packages have a pretty large header, which means less efficiency.
• Even worse, it's TCP-based, which means that there are sequence numbers and retransmissions, which can lead to queueing and latency, and the bigger the environment is, the more you usually feel these effects affect your virtual machine performance.

That being said, the fact that it's based on an Ethernet stack makes it easier to deploy iSCSI-based solutions, while at the same time offering some unique challenges. For example, sometimes it's difficult to explain to a customer...