Windows Server

Windows Server 2008 : Configuring Server Storage (part 1)

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10/22/2010 5:56:03 PM

Understanding Server Storage Technologies

As the demand for server storage has grown, so too has the number of new storage technologies. Over the years, the range of server storage options has broadened from simple direct-attached storage (DAS) to network-attached storage (NAS) and, most recently, to Fibre Channel (FC) and iSCSI SANs.

Direct-Attached Storage

DAS is storage attached to one server only. An example of a DAS solution is a set of internal hard disks within a server or a rack-mounted RAID that is connected to a server through a SCSI or FC controller. The main feature of DAS is that it provides a single server with fast, block-based data access to storage directly through an internal or external bus. (Block-based, as opposed to file-based, means that data is moved in unformatted blocks rather than in formatted files.) DAS is an affordable solution for servers that need good performance and do not need enormous amounts of storage. For example, DAS is often suitable for infrastructure servers such as DNS, WINS and DHCP servers, and domain controllers. File servers and Web servers can also run well on a server with DAS.

The main limitation of DAS is that it is directly accessible from a single server only, which leads to inefficient storage management. For example, Figure 1 shows a LAN in which all storage is attached directly to servers. Despite the fact that the Web and App2 servers have excess storage, there is no easy way for these resources to be redeployed to either the Mail or App1 server, which need more storage space.

Figure 1. A network with only a DAS solution

Managing DAS in Windows Server 2008

The main tool used for managing DAS in Windows is the Disk Management console. This tool, which you can access in Server Manager, enables you to partition disks and format volume sets. You can also use the Diskpart.exe command-line utility to perform the same functions available in Disk Management and perform additional functions as well.

Network-Attached Storage

NAS is self-contained storage that other servers and clients can easily access over the network. A NAS device or appliance is a preconfigured server that runs an operating system specifically designed for handling file services. The main advantage of NAS is that it is simple to implement and can provide a large amount of storage space to clients and servers on a LAN. The downside of NAS is that, because your servers and clients access a NAS device over the LAN as opposed to over a local bus, access to data is slower and file-based as opposed to block-based. NAS performance is, therefore, almost always slower than that of DAS.

Because of its features and limitations, NAS is often a good fit for file servers, Web servers, and other servers that don’t need extremely fast access to data.

Figure 2 shows a network in which clients use a NAS appliance as a file server.

Figure 2. A LAN with a NAS appliance

Managing NAS

NAS appliances come with their own management tools, which are typically Web based.

Storage-Area Networks

SANs are high-performance networks dedicated to delivering block data between servers and storage subsystems. From the point of view of the operating system, SAN storage appears as if it were installed locally. The most important characteristic that distinguishes a SAN from DAS is that in a SAN, the storage is not restricted to one server but is, in fact, available to any of a number of servers. (SAN storage can be moved from server to server, but outside of clustered file system environments, it is not accessible by more than one server at a time.)

Note: SAN vs. DAS

Although DAS data transfer rates are typically faster than those of a SAN, the performance gap between DAS and SAN technologies is constantly shrinking. Despite the bus speed advantage offered by DAS, SANs are still considered preferable because the advantage SANs offer of shared storage outweighs the shortcoming of slightly lower access speeds.

A SAN is made up of special devices, including HBAs on the host servers, switches that help route storage traffic, disk storage subsystems, and tape libraries. These hardware devices that connect servers and storage in a SAN are called the SAN fabric. All these devices are then interconnected by fiber or copper. Once connected to the fabric, the available storage is divided up into virtual partitions called logical unit numbers (LUNs), which then appear to servers as local disks.

SANs are designed to enable centralization of storage resources while eliminating the distance and connectivity limitations posed by DAS. For example, parallel SCSI bus architecture limits DAS to 16 devices at a maximum (including the controller) distance of 25 meters. Fibre Channel SANs extend this distance limitation to 10 km or more and enable an essentially unlimited number of devices to attach to the network. These advantages enable SANs to separate storage from individual servers and to pool unlimited storage on a network where that storage can be shared.

SANs are a good solution for servers that require fast access to very large amounts of data (especially block-based data). Such servers can include mail servers, backup servers, streaming media servers, application servers, and database servers. The use of SANs also allows for efficient long distance data replication, which is typically part of a disaster recovery (DR) solution.

Figure 3 illustrates a simple SAN.

Figure 3. A sample storage-area network (SAN)

SANs generally occur in two varieties: Fibre Channel and iSCSI.

Fibre Channel SANs

Fibre Channel (FC) delivers high-performance block input/output (I/O) to storage devices. Based on serial SCSI, FC is the oldest and most widely adopted SAN interconnect technology. Unlike parallel SCSI devices, FC devices do not need to arbitrate (or contend) for a shared bus. FC instead uses special switches to transmit information between multiple servers and storage devices at the same time.

The main advantage of FC is that it is the most widely implemented SAN technology and has, at least until recently, offered the best performance. The disadvantages of FC technology are the cost of its hardware and the complexity of its implementation. Fibre Channel network components include server HBAs, cabling, and switches. All these components are specialized for FC, lack interoperability among vendors, are relatively expensive, and require special expertise.

Internet SCSI (iSCSI) is an industry standard developed to enable transmission of SCSI block commands over an Ethernet network by using the TCP/IP protocol. Servers communicate with iSCSI devices through a locally installed software agent known as an iSCSI initiator. The iSCSI initiator executes requests and receives responses from an iSCSI target, which itself can be the end node storage device or an intermediary device such as a switch. For iSCSI fabrics, the network also includes one or more Internet Storage Name Service (iSNS) servers that, much like DNS servers on a LAN, provide discoverability and zoning of SAN resources.

By relying on TCP/IP, iSCSI SANs take advantage of networking devices and expertise that are widely available, a fact that makes iSCSI SANs generally simpler and less expensive to implement than FC SANs.

Aside from lower cost and greater ease of implementation, other advantages of iSCSI over FC include:

  • Connectivity over long distances Organizations distributed over wide areas might have a series of unlinked “SAN islands” that the current FC connectivity limitation of 10 km cannot bridge. (There are new means of extending Fibre Channel connectivity up to several hundred kilometers, but these methods are both complex and costly.) In contrast, iSCSI can connect SANs in distant offices by using in-place metropolitan area networks (MANs) and (wide-area networks) WANs.

  • Built-in security No security measures are built into the Fibre Channel protocol. Instead, security is implemented primarily through limiting physical access to the SAN. In contrast to FC, the Microsoft implementation of the iSCSI protocol provides security for devices on the network by using the Challenge Handshake Authentication Protocol (CHAP) for authentication and the Internet Protocol security (IPSec) standard for encryption. Because these methods of securing communications already exist in Windows networks, they can be readily extended from LANs to SANs.

Note: iSCSI SAN fabric

An iSCSI SAN can use dedicated devices for its fabric, or it can rely on an organization’s existing LAN, MAN, or WAN infrastructure. For both security and performance, a dedicated iSCSI network separating network traffic from storage traffic is recommended.

The main disadvantage of an iSCSI SAN is that, unless it is built with dedicated (and expensive)10-GB Ethernet cabling and switches, the I/O transfer of iSCSI is slower than an FC-based SAN can deliver. And if indeed you do choose to use 10-GB equipment for your iSCSI SAN instead of the much more common choice of gigabit Ethernet, the high cost of such a 10-GB solution would eliminate the price advantage of iSCSI relative to FC.

Exam Tip

Vocabulary terms you should understand for the exam include LUNs, HBA, iSCSI initiator, iSCSI target, SAN fabric, and iSNS.

Managing SANs

Windows Server 2008 includes the Virtual Disk service (VDS), an application programming interface (API) that enables FC and iSCSI SAN hardware vendors to expose disk subsystems and SAN hardware to administrative tools in Windows. When vendor hardware includes the VDS hardware provider, you can manage that hardware within Windows Server 2008 by using tools such as Disk Management, Storage Manager for SANs (SMfS), Storage Explorer, iSCSI Initiator, or the command-line tool DiskRAID.exe.

  • SMfS SMfS is available in Windows Server 2008 as a feature that you can add through the Add Features Wizard. You can use SMfS to manage SANs by provisioning disks, creating LUNs, and assigning LUNs to different servers in the SAN.

    Figure 4 shows the SMfS console.

    Figure 4. Storage Manager for SANs

  • Storage Explorer Storage Explorer is available by default in Windows Server 2008 through the Administrative Tools program group. You can use Storage Explorer to display detailed information about servers connected to the SAN as well as about fabric components such as HBAs, FC switches, and iSCSI initiators and targets. You can also use Storage Explorer to perform administrative tasks on an iSCSI fabric.

  • iSCSI Initiator The iSCSI Initiator tool is available by default in Windows Server 2008 through the Administrative Tools program group. This tool enables you to configure security, discovery, and other features of the local server connections to iSCSI targets.

  • DiskRAID DiskRAID is a command-line tool that enables you to manage LUNs in a VDS-enabled hardware RAID.

Other -----------------
- Use the Microsoft Management Console (MMC)
- Manage Windows Server 2008 : Work with Preconfigured MMCs
- Manage Windows Server 2008 : Work with the Task Scheduler
- Manage Windows Server 2008 Using Remote Desktop
- Manage Windows Server 2008: Configure Backups and Perform Restores
- Windows Server 2008 : Determine Which Terminal Services Roles to Install
- Windows Server 2008 : Install the TS Gateway Role Service and TS Web Access Role Service
- Windows Server 2008 : Install the TS Licensing Role Service
- Windows Server 2008 : Install the Terminal Server Role Service
- Windows Server 2008 : Configure a Load-Balanced Farm with TS Session Broker
- Windows Server 2008 : Configure the TS Gateway Manager
- Windows Server 2008 : Configure the TS RemoteApp Manager
- Windows Server 2008 : Manage Terminal Services
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