Chris McCain - Mastering VMware® Infrastructure3

Once you have mastered the differences among the various architectures and identified the features of each that are most relevant to your data and virtual machines, you can feel confident in your decision. Equipped with the right information, you will be able to identify a solid storage platform on which your virtual infrastructure will be scalable, efficient, and secure.

The storage adapters in ESX Server will be identified automatically during the boot process and are available for configuration through the VI client or by using a set of command-line tools. The storage adapters in your server must be compatible. Remember to check the VI3 I/O Compatibility Guide before adding any new hardware to your server. You can find this guide at VMware's website (http://www.vmware.com/pdf/vi3_io_guide.pdf).

In the following sections, we'll cover both sets of tools, command line and GUI, and explore how to use them to create and manage the various storage types. Figure 4.2 and Figure 4.3 show the Virtual Infrastructure (VI) Client's configuration options for storage adapters and storage, respectively.

Figure 4.2Storage adapters in ESX Server are found automatically because only adapters certified to work with VMware products should be used. Consult the appropriate guides before adding new hardware.

Figure 4.3The VI Client provides an easy-to-use interface for adding new datastores located on fibre channel, iSCSI, or NAS storage devices.

A storage area network (SAN) is a communication network designed to handle the block-level transfer of data between a storage device and the requesting servers or hosts. The block-level transfer of data makes for highly efficient and highly specialized network communication that enables the reliable, low-latency transfer of large amounts of data with minimal server overhead.

A SAN consists of several components that direct and manage the flow of data across the dedicated network. These components reside in one of three segments on the SAN:

♦ The hosts accessing the storage

♦ The network across which traffic runs

♦ The storage

The concepts of a storage area network have long revolved around using a Fibre Channel protocol for communication among nodes connected to the network. However, recently the quick adoption of iSCSI storage area networks has introduced a strong competitor to its fibre channel predecessor. Whereas fibre channel storage networks use the Fibre Channel Protocol (FCP) for communication among nodes, iSCSI provides a similar block-level data transfer over standard IP networks.

As your virtualization career moves forward, you will, at some point, most certainly be in a position where you must understand and differentiate between the two most popular SAN architectures today: Fibre Channel and iSCSI. Both architectures offer significant benefits in the areas of reliability, redundancy, scalability, performance, and security. Incorporating a shared storage back-end helps eliminate many of the network failure issues that administrators find themselves constantly fixing. ESX Server with a back-end SAN offers:

♦ Automatic failover and multipathing at the host bus adapter (HBA) and storage port

♦ A high-performance file system in VMFS-3

♦ VMotion, Distributed Resource Scheduler (DRS), and High Availability (HA)

♦ Support for Microsoft Cluster Services (MSCS)

♦ VMware Consolidate Backup (VCB)

SAN devices offer additional benefits in the areas of storage replication and mirroring. Using third-party software, you can replicate or mirror the data on your LUNs to other LUNs on the same or even different storage devices. This feature offers administrators great possibilities in the areas of disaster recovery and business continuity.

After you finish your debate on fibre channel versus iSCSI and you purchase one or the other, you will then have to spend some time devising the proper procedure for managing and implementing LUNs. We are discussing LUN creation and management separately from the fibre channel and iSCSI sections because of its independence from the actual storage architecture. Details on the configuration of fibre channel and iSCSI will follow.

A logical unit number (LUN) is a logical configuration of disk space carved from an underlying set of physical disks. The physical disks on which LUNs are configured are most often arranged as a Redundant Array of Independent Disks (RAID) to support performance and/or redundancy for the data to be stored on the LUN. This section will look at RAID architectures, LUN addressing, and the age-old question of many little LUNs versus fewer big LUNs.

No matter your storage device, fibre channel or iSCSI, you will need to create LUNs, or at least work closely with someone who will create LUNs for you. Virtual machine performance can, in some cases, come down to a matter of having a solid LUN strategy in place for the activity level of that VM. Choosing the right RAID level for a LUN is therefore an integral part of your VI3 implementation. The most common types of RAID configurations are:

RAID 0 Disks configured in RAID 0 do not offer any type of redundancy or protection against drive failure. RAID 0 does, however, provide the fastest performance times because data is written simultaneously to all drives involved. A RAID 0 volume, also commonly referred to as a stripe, can have two or more disks as part of the array. Figure 4.4 outlines the structure of a RAID 0 configuration.

Figure 4.4A RAID 0 disk configuration provides high-speed performance for data stored across a series of disks.

RAID 1 A RAID 1 configuration puts two identically sized allocations of space from two drives together for the provisioning of a backup strategy that allows for either of the drives to fail and still maintain data. A RAID 1 volume, also commonly referred to as a mirrored array, loses 50 percent of the available drive space. For example, two 500GB LUNs configured as a RAID 1 array will only provide 500GB of storage. Figure 4.5 outlines the structure of a RAID 1 configuration.

Figure 4.5A RAID 1 disk array, or mirrored volume, provides redundancy in the event of a single drive failure. A RAID 1 array is the most expensive disk type because it incurs a 50 percent loss in the amount of storage.

RAID 5 A RAID 5 array writes data and parity simultaneously to all drives involved in the array. RAID 5 arrays provide redundancy in the event of a single drive failure by writing parity in equal increments across all drives. Parity is a mathematical calculation that allows N-1 drives the ability to make up the data on any other drive. A RAID 5 is the most efficient array when looking at disk space loss. The RAID 5 array only loses one drive's worth of space. For example, a RAID 5 array made up of four 250GB hard drives will have approximately 750GB of storage space available. Figure 4.6 outlines the structure of a RAID 5 configuration.

Figure 4.6A RAID 5 array is commonly used because of its data protection and limited loss of space. Both data and parity are written equally across all drives in the array.