The storage design that is utilized for the host server architecture has a major impact on host and guest performance. Storage performance is a complicated mix of drive, interface, controller, cache, protocol, SAN, HBA, driver, and operating system considerations. The overall performance of the storage architecture is typically measured in terms of Maximum Throughput, Maximum IO operations per second (IOPS), and Latency or Response Time. While each of the three factors is important, IOPS and Latency are the most relevant to server virtualization.
This section outlines the various storage architecture considerations and provides recommendations for each of the overall architecture patterns.
Storage Connectivity Individual disks and storage arrays can be accessed by host servers in three
different ways: Direct Attached Storage, iSCSI Storage Area Networks, and Fibre Channel Storage Area Networks.
Direct Attached Storage Direct attached storage typically consists of hard drives internal to the host
server itself or hard drives housed in a dedicated storage array attached directly to the server via SCSI, SAS, or eSATA connections. The host server utilizes an internal SCSI, SAS, or SATA controller card to enable the server to access the storage and enable various RAID levels. The storage array is typically dedicated to the individual server.
iSCSI Storage Area Network iSCSI is an increasingly popular storage networking architecture that enables use
of the SCSI protocol over TCP/IP network infrastructures. iSCSI enables the use of standard Ethernet networking components such as NICs, Switches, and Routers to build a storage area network. Typically iSCSI SANs are less expensive to implement than traditional Fibre Channel SANs. The storage array used in iSCSI architecture is usually a low- to mid-range array that is shared by multiple host servers. Redundant, dedicated gigabit Ethernet NICs are recommended for iSCSI connectivity.
Fibre Channel Storage Area Network Fibre Channel storage area networks provide high speed, low latency
connectivity to storage arrays. Host Bus Adapters (HBAs) are utilized by the host servers to connect to the Fibre Channel SAN via switches and directors. Fibre Channel SANs are typically used in concert with mid to high end storage arrays, which provide a multitude of features such as RAID, disk snapshots, multipath IO, and so on.