What is a storage area network? SAN explained (2023)

What are storage area networks used for?

Simply put, a SAN is a network of disks that is accessed by a network of servers. There are several popular uses for SANs in enterprise computing. A SAN is typically used to consolidate storage. For example, it is common for a computer system, such as a server, to include one or more local storage devices. But consider a data center with hundreds of servers, each running virtual machines that can be deployed and migrated between servers as desired. If a workload's data is stored in this local storage, the data may also need to be moved if the workload is migrated to another server, or restored if the server fails. Rather than attempt to organize, track, and use the physical disks located on individual servers throughout the data center, an enterprise may choose to move storage to a dedicated storage subsystem, such as a storage array, where it can be provisioned, managed, and managed. and protect storage. .

A SAN can also improve storage availability. Since a SAN is essentially a network fabric of interconnected computers and storage devices, an outage in one network path can usually be overcome by enabling an alternate path through the SAN fabric. Therefore, the failure of a single cable or device does not leave storage inaccessible to enterprise workloads. Additionally, the ability to treat storage as a collective resource can improve storage utilization by eliminating "forgotten" disks on underutilized servers. In contrast, a SAN provides a central location for all storage and allows administrators to group and manage storage devices together.

All of these use cases can improve an organization's regulatory compliance, disaster recovery (DR), and business continuity (BC) postures, improving IT's ability to support enterprise workloads. But to appreciate the value of SAN technology, it's important to understand how a SAN differs from a traditional DAS.

With DAS, one or more drives are directly attached to a specific computer through a dedicated storage interface, such as SATA or SAS. Disks are generally used to store applications and data that are meant to run on that specific server. Although DAS devices on a server can be accessed from other servers, the communication takes place over the common IP network, the LAN, along with traffic from other applications. Accessing and moving large amounts of data across the IP network on a daily basis can be time consuming, and the bandwidth demands of large data movements can affect the performance of applications on the server.

A SAN operates in a profoundly different way. SAN interconnects all disks in a dedicatedstorage areagrid. This dedicated network exists separate and separate from the normal LAN. This approach allows any of the SAN-attached servers to access any of the SAN-attached disks, effectively treating the storage as a single collective resource. None of the SAN storage data needs to go over the LAN, mitigating LAN bandwidth needs and preserving LAN performance. Since the SAN is a separate dedicated network, the network can be designed to emphasize performance and resiliency, which are beneficial for business applications.

A SAN can support a large number of storage devices, and the storage arrays (purpose-built storage subsystems) that support a SAN can scale to store hundreds or even thousands of disks. Similarly, any server with a suitable SAN interface can access the SAN and its vast storage potential, and a SAN can support many servers. There are two main types of network technologies and interfaces used for SANs:Fiber channel and iSCSI.

1. FibraCanal. FCis a high-speed network known for its high performance and low latency, offering data speeds of up to 128 Gbps over distances of metropolitan areas (up to about 6 miles or 10 km) when using fiber optic cables and interfaces. This type of dedicated network potentially allows block-level storage to be consolidated in one location, while servers can be spread across campus buildings or across a city. Traditional copper cabling and corresponding FC interfaces can also be used when storage and servers are co-located and the distances do not exceed 100 feet (10 meters). More recently, the FC name and performance designations were changed to Gigabit FC and the latest iterations of the interface promise 128 and 256 GFC respectively. As a network interface, FC supports multiple topologies, including point-to-point, arbitrated loop, and switched fabric, like modern Ethernet. FC is implemented by deploying FC host bus adapters (HBAs) in each FC server, storage or network switches, or other network devices. Each HBA includes one or more ports where data is exchanged. Ports can be virtual or physical, and physical ports are interconnected by cables, allowing HBAs and switches to form a network fabric.
2. ISCSI.iSCSI esanother type of networkit is meant to connect computing with shared storage. It can work at speeds of up to 100 Gbps, but it provides a number of simplifications for data center operators. While FC offers a unique and highly specialized network design, iSCSI combines traditional SCSI block data and command packets with common Ethernet and TCP/IP network technology. This allows iSCSI storage networks to use the same cabling, network adapters, switches, and other network components used in any Ethernet network; In many cases, iSCSI can operate on the same Ethernet LAN, without a separate LAN, and can exchange data across LANs, WANs, and even the Internet. Each server's operating system views iSCSI data access simply as another locally attached SCSI drive. ISCSI operates using the concepts of initiators and targets. An initiator is typically a server that participates in the iSCSI SAN and sends SCSI commands over an IP network. Initiators can be software-based, like an operating system, or hardware-based, like a storage array. A destination is typically a storage resource, such as a dedicated network-attached hard drive storage device, but it can also be another computer.

How a SAN works

A SAN is essentially a network designed to connect servers with storage. The goal of any SAN is to remove storage from individual servers and allocate storage collectively where storage resources can be centrally managed and protected. This centralization can be accomplished physically, such as placing disks in a dedicated storage subsystem, such as a storage array. But centralization can also be handled more and more logically through software, such as VMware vSAN, which relies on virtualization to find and pool available storage.

By connecting collective storage to servers through a separate network, beyond the traditional LAN, storage traffic performance can be optimized and accelerated because storage traffic no longer has to compete for LAN bandwidth. needed by servers and their workloads. Therefore, enterprise workloads can potentially gain faster access to staggering amounts of storage. A SAN is generally perceived as a series of three distinct layers: a host layer, a fabric layer, and a storage layer. Each layer has its own components and characteristics.

1. host layer.The host layer represents the servers connected to the SAN. In most cases, the hosts (servers) run business workloads, such as databases, that require access to storage. Hosts often use traditional LAN (Ethernet) components to allow the server and its workload to communicate with other servers and with users. However, SAN hosts also come with a separate network adapter dedicated to SAN access. The network adapter used for most FC SANs is called a Host Bus Adapter (HBA). Like most network adapters, the FC HBA uses firmware to operate the HBA hardware, as well as a device driver that connects the HBA to the server's operating system. This configuration allows the workload to communicate commands and storage data through the operating system to the SAN and its storage resources. FC is one of the most popular and powerful.Available SAN Technologies, but other widely accepted SAN technologies include InfiniBand along with iSCSI. Each technology represents its own matrix of costs and trade-offs, so the organization must carefully consider its workload and storage needs when selecting a SAN technology. Finally, the host, fabric, and storage layers must share the same SAN technology.
2. Cloth cape.The fabric layer represents the cabling and network devices that make up the network fabric that interconnects SAN hosts and SAN storage. SAN network devices within the fabric layer may includeSAN switches, gateways, routers, and protocol bridges. The cabling and corresponding ports of the SAN fabric devices can use fiber optic connections, for long-range network communication, or traditional copper cables for terrestrial-range LAN communication. The difference between aredis abodyit is redundancy: the availability of multiple alternate paths from hosts to storage throughout the fabric. When creating a SAN fabric, multiple connections are usually implemented to provide multiple paths. If a path is damaged or interrupted, SAN communication will use an alternate path.
3. Storage layer.The storage tier is made up of multiple storage devices collected into multiple storage groups, tiers, or types. Storage typically involves traditional magnetic HDDs, but can also include SSDs along with optical media devices such as CD and DVD drives and tape drives. Most storage devices on a SAN are organized into physical RAID groups that can be used to increase storage capacity, improve storage device reliability, or both. Logical storage entities, such as RAID groups or even disk partitions, are each given a unique LUN that serves the same basic purpose as a drive letter such as C or D. Therefore, any SAN host can access potentially to any SAN LUN on the SAN Fabric. By organizing storage resources and designating storage entities in this way, an organization can allow host access to specific LUNs, allowing it to exercise granular control over the organization's storage assets. There are two basic methods for controlling SAN permissions: LUN masking and zoning. The mask is essentially a list of LUNs that are not available or should not be accessed by a SAN host. Compared,zoning controls host accessLUNs by configuring the fabric itself, limiting host access to storage LUNs that are in an approved and permitted SAN zone.

A SAN also employs a series of protocols that allow software to communicate or prepare data for storage. The most common protocol is Fiber Channel Protocol (FCP), which maps SCSI commands onto FC technology. iSCSI SANs will employ an iSCSI protocol that maps SCSI commands over TCP/IP. But there are other protocol combinations, such as ATA over Ethernet, which maps ATA storage commands over Ethernet, as well asFiber Channel over Ethernet (FCoE)and other less-used protocols, including iFCP, which maps FCP over IP, and iSCSI Extensions to RDMA, which maps iSCSI over InfiniBand. SAN technologies often support multiple protocols, helping to ensure that all layers, operating systems, and applications can communicate efficiently.

Storage Area Network Configuration

To integrate all SAN components, a company must first meet the vendor's hardware and software compatibility requirements:

• host bus adapters (firmware version, driver version, and patch list);
• change (firmware); me
• storage (firmware, host personality firmware, and patch list).

So to configure the SAN you need to do the following:

1. Assemble and connect all hardware components and install the corresponding software.
   1. Check the versions.
   2. Configure the HBA.
   3. Configure the storage array.
2. Change configuration settings as necessary.
3. Test the integration.
1. Test all operational processes for the SAN environment, including normal production processing, failure mode testing, and backup.
4. Establish a performance baseline for each component as well as the entire SAN.
5. Document SAN installation and operating procedures.

Architecture and operation of the SAN fabric

The core of a SAN is its fabric: the high-performance, scalable network that interconnects hosts (servers) and storage devices or subsystems. The fabric design is directly responsible for the reliability and complexity of the SAN. In its simplest form, an FC SAN can simply connect HBA ports on servers directly to corresponding ports on SAN storage arrays, often using optical cables for maximum speed and support for networking over greater physical distances.

But these simple connectivity schemes protect the true power of a SAN. In practice, the SAN fabric is designed to improve storage reliability and availability by eliminating single points of failure. A central strategy in designing a SAN is to employ a minimum of two connections between any SAN element. The goal is to ensure that at least one working network path is always available between SAN hosts and SAN storage.

Consider a simple example in the image above, where two SAN hosts need to communicate with two SAN storage subsystems. Each host uses a separate HBA, not a multi-port HBA because the HBA device itself is a single point of failure. The port of each HBA is connected to a port on a different SAN switch, such asfiber channel switch. Similarly, multiple ports on the SAN switch connect to different target systems or storage devices. This is a simple redundant mesh; remove any1connection in the diagram, andBothservers can still communicate withBothstorage systems to preserve storage access for workloads on both servers.

Consider the basic behavior of a SAN and its fabric. A host server requires access to SAN storage; the host will internally create a request to access the storage device. Traditional SCSI commands used for storage access are encapsulated in packets for the network (in this case, FC packets), and the packets are structured according to the rules of the FC protocol. The packets are delivered to the host HBA, where they are placed on the network's copper or optical cables. The HBA transmits the request packets to the SAN, where the request will reach the SAN switches. One of the switches will receive the request and send it to the corresponding storage device. In a storage array, the storage processor will receive the request and interact with the storage devices within the array to accommodate the request from the host.

Description of SAN switches

The SAN switch is the focal point of any SAN. Like most network switches, the SAN switch receives a data packet, determines the source and destination of the packet, and forwards it to the intended destination device. Ultimately, the topology of the SAN fabric is defined by the number of switches, the type of switches, such as trunk switches or modular or edge switches, and the way the switches are interconnected. Smaller SANs can use modular switches with 16, 24, or even 32 ports, while larger SANs can use trunk switches with 64 or 128 ports. SAN switches can be combined to create large and complex SAN fabrics connecting thousands of servers and storage devices.

A fabric by itself is not enough to guarantee resistance to storage. In practice, storage systems must include a variety of embedded technologies, including RAID (pooling disks for increased capacity and resiliency) with robust error handling and self-healing capabilities. The storage system often adds more technologies for efficient storage utilization, including thin provisioning, storage snapshots or cloning, deduplication, and data compression. While a well-designed SAN fabric allows any host to reach any storage device, isolation techniques such as zoning and LUN masking can be used to restrict host access to certain LUNs to improve performance and reliability. storage security on the SAN.

Alternative SAN approaches

While SAN technology has been available for decades, there are a number of dedicated enhancements and enhancements that reshape SAN design and implementation. These alternatives include virtual SAN, unified SAN, converged SAN, and hyperconverted infrastructure (HCI).

• virtual SANs.Virtualization technology was a perfect fit for the SAN, encompassing storage capabilities and storage networking to add flexibility and scalability to the underlying physical SAN. Avirtual SANs-- denoted by a capital V in VSAN -- is a form of isolation, reminiscent of traditional SAN zoning, which essentially uses virtualization to create one or more logical partitions or segments within the physical SAN. Traditional VSANs can use this isolation to manage SAN network traffic, improve performance, and enhance security. Therefore, Virtual SAN isolation can prevent potential problems on one SAN segment from affecting other SAN segments, and segments can be logically changed as needed without touching any physical SAN components.VMware offers virtual SAN technology-- denoted by a lowercase v in vSAN -- which builds on basic VSAN approaches to provide advanced features including storage pooling or tiering -- storage discovery and organization between hosts -- along with migration Seamless Data Transfer -- Move storage from one platform to another without downtime for applications that depend on this data. VMware vSAN can also accommodate features such as information lifecycle management, allowing vSAN to automatically move data from one storage performance tier to another, depending on how the data is accessed. For example, frequently accessed data may be placed in a high-performance storage tier, then moved to a lower tier as the data is less accessed, and finally relegated to a lower performance storage tier. file when data deteriorates.

• SAN Unified.A SAN is known for its support for block storage, which is typical of business applications. But files, objects, and other types of storage traditionally require a separate storage system, such as network-attached storage (NAS). A SAN that supportsunified storageIt is capable of supporting multiple approaches, such as file, block, and object-based storage, within the same storage subsystem. Unified storage provides these capabilities by handling multiple protocols, including file-based SMB and NFS, as well as block-based ones like FC and iSCSI. By using a single storage platform for block and file storage, users can take advantage of powerful features typically reserved for traditional block-based SANs, such as storage snapshots, data replication, storage tiering, encryption data, data compression, data and data deduplication. However, different storage protocols place varying demands on the storage system, sometimes resulting in variable storage performance. For example, file-based data access can take longer and be more random than block-based data access. The changing demands of unified storage systems may not be desirable for some enterprise-class applications, yet they can still benefit from the dedicated performance characteristics of block-based SAN.

• Converged SAN.A common disadvantage of a traditional FC SAN is the cost and complexity of a separate network dedicated to storage. ISCSI is a way to overcome the cost of a SAN by using common Ethernet network components instead of FC components. FCoE supports a converged SAN that can run FC communication directly over Ethernet network components, converging common IP and FC storage protocols into a single, low-cost network. FCoE works by encapsulating FC frames within Ethernet frames to route and transport FC data over an Ethernet network. However, FCoE relies on end-to-end support across network devices, which has been difficult to achieve in general, limiting the choice of providers. In addition, FCoE changes the way networks are deployed and managed, especially authentication and corporate data security, and organizations have been reluctant to make such changes to traditional policies and processes.

• Hyperconverted infrastructure.HCI data center usage has grown dramatically in recent years. HCI combines compute and storage resources into pre-packaged modules, allowing modules, also called nodes, to be added as needed and managed through a single, common utility. HCI employs virtualization, which abstracts and pools all computing and storage resources. IT administrators provision virtual machines and storage from pools of available resources. The fundamental goal of HCI is to simplify hardware deployment and management while enabling rapid scalability. HCI 2.0 unbundles storage from compute resources, essentially providing storage and compute on their own nodes, so compute and storage can scale separately, but the underlying goals are the same. HCI is not a SAN, butcan be used instead of SANor even coexist with traditional enterprise SANs, depending on the demands of core enterprise workloads.

SAN Benefits

Whether traditional or virtual, aSAN offers several attractive benefitsthat are vital for enterprise-class workloads.

• High performance.The typical SAN uses a separate network fabric that is dedicated to storage tasks. Fabric is traditionally FC for superior performance, although iSCSI and converged networking are also available.
• High scalability.SAN can support extremely large deployments spanning thousands of SAN host servers and storage devices or even storage systems. New hosts and storage can be added as needed to build the SAN to meet specific organization requirements.
• High availability.A traditional SAN is based on the idea of ​​a mesh network that ideally interconnects everything with everything else. This means that a full-featured SAN implementation does not have a single point of failure between a host and a storage device, and communication across the fabric can always find an alternate path to maintain storage availability for load loads. worked.
• Advanced management features.A SAN will support a variety of useful enterprise-class storage features, including data encryption, data deduplication, storage replication, and self-healing technologies designed to maximize storage capacity, security, and resiliency. data. Resources are almost universally centralized and can easily be applied to all storage resources on the SAN.

Disadvantages of SANs

But despite the benefits,SANs are not perfect, and there are a variety of potential pitfalls IT leaders should consider before implementing or upgrading a SAN.

• Complexity.While there are more convergence options such as FCoE and unified options for SANs today, traditional SANs present the added complexity of a second network, complete with expensive dedicated HBAs on host servers, switches, and cabling within a complex fabric and storage. and redundant. processor ports on storage arrays. These networks must be carefully designed and monitored, but the complexity is increasingly problematic for IT organizations with fewer employees and smaller budgets.
• Scale.Considering the cost, a SAN is generally only effective in larger, more complex environments where there are many servers and significant storage. It is certainly possible to implement a SAN on a small scale, but the cost and complexity are hard to justify. Smaller implementations can often achieve satisfactory results using an iSCSI SAN, a converged SAN on a single common network, such as FCoE, or an HCI implementation, which specializes in pooling and provisioning resources.
• Management.with the idea ofcomplexityCentered on hardware, there is also a significant challenge in managing SANs. Configuring features like LUN mapping or zoning can be problematic for busy organizations. Configuring RAID and other self-healing technologies, as well as the corresponding logging and reporting, not to mention security, can be time consuming, but they are unavoidable in order to maintain BC, DR and organization compliance postures.

SAN x NAS

Network Attached Storage (NAS) is an alternative means of storing and accessing data that relies on file-based protocols, such as SMB and NFS, instead of block-based protocols, such as FC and iSCSI, used on SANs. there is anotherdifferences between a SAN and a NAS. While a SAN uses a network to connect servers and storage, a NAS relies on a dedicated file server located between the servers and storage.

While both approaches store data, the choice of system will depend on the type of data being handled. A SAN is the preferred choice for block-based data storage, which generally lends itself well to structured data, such as storage for enterprise-class relational database applications. By comparison, a NAS, with its file-based approach, is better suited for unstructured data such as document files, emails, images, videos, and other common file types.

Like a SAN, a NAS consolidates storage into a single location and can support data management and protection tasks such as data backup and archiving. However, a NAS uses a common network and requires much lower cost and complexity than SANs. However, SANs shine with raw performance and scalability, capable of delivering the best performance for the most demanding business applications.

SAN and NAS are not mutually exclusive. A SAN and NAS can coexist in the same data center where file and block-based data storage is required. BothSAN and NAS implementations can be upgradedto increase performance, simplify management, combat the IT shadow, and address storage capacity constraints. In some cases, separate storage systems can be replaced with a unified storage system or the SAN can be simplified by using an iSCSI SAN.

Main suppliers and products

Do not missvendors and products to support enterprise SANimplementations. When planning a SAN, architects often consider the hosts (servers), the network (fabric), components, and storage subsystems.

Hosts.Any host can operate on the SAN, but each host server requires a suitable network interface to access the fabric. Enterprise-class servers can be purchased with multi-port FC HBAs already installed, a common tactic for technology upgrade projects. If the servers do not already come with an HBA, an HBA can be added as a server upgrade project. However, adding an HBA as an aftermarket upgrade will require an available PCIe slot on the server motherboard. IT staff should investigate each target server and ensure that a suitable upgrade slot is physically available before purchasing and proceeding with upgrades. Additionally, such upgrades will require the server to be shut down, so IT staff must schedule server downtime and plan for such disruptive upgrades.

HBA cardsthey are commonly built on communication chips from technology leaders such as Agilent, ATTO, Broadcom, Brocade and QLogic. Actual HBAs are manufactured and sold through many technology vendors and procurement channels.

Red.The SAN fabric itself is made up of copper or optical cabling, as well as network components such as network switches. As with HBAs, appropriate cabling is readily available through common procurement channels and technology vendors. Both edge and director switches can be found based on technologies used by major chip and technology manufacturers. Examples include the following:

• ATTO Technology 8308, 8316 and 8324 switches;
• Brocade G-series switches and DCX-series directors;
• Cisco MDS Series Switches, Nexus 5672UP, and MDS Series Directors;
• Juniper QFabric QFX series switches; Y
• QLogic SANbox 5xxx series switches and SANbox 9xxx directors.

To stock.Storage arrays excel in the SAN because storage is the heart of SAN technology, and storage subsystems have many of the features (deduplication, replication, etc.) that make SANs so attractive to the enterprise. Here is a sampling of the leading storage array vendors:

• Dell EMC offers several major product lines, including Isilon NAS storage, EMC Unity hybrid flash storage arrays for file and block storage, SC series arrays, and VMAX storage products.
• Hitachi Data Systems offers Hitachi NAS Platform and G Series arrays.
• Hewlett Packard Enterprise product lines include entry-level HPE StoreEasy Storage NAS systems and flash-enabled MSA storage, as well as mid-range HPE 3PAR StoreServ arrays.
• Huawei offers OceanStor Dorado V3 all-flash arrays and OceanStor 18000 V5 hybrid flash storage systems.
• IBM has disk and flash storage arrays, including the DS family, XIV family, and Scale Out Network Attached Storage system, as well as numerous variations of its FlashSystem family.
• NetApp offers low latency NVMe-over-Fabrics support for its all-flash arrays andsupports hybrid cloud data tiersin your OnTap storage software.

Other notable SAN storage vendors include Fujitsu, Lenovo, Oracle, and Western Digital. Newer SAN vendors that focus on all-flash storage include Kaminario, Pure Storage, IntelliFlash, formerly Tegile, and Violin Systems.

When it comes to storage, don't overlook the potential value of SAN-as-a-Service. The idea issimilar in principle to any cloudor the SaaS offer, which issold to customers as a managed service. A vendor builds and manages a SAN, and then sells capacity on that SAN to outside customers. The provider is responsible for creating and maintaining the SAN, and its functions, such as replication, and customers can access one or more LUNs created for them on the provider's SAN, typically for a recurring monthly fee. SAN services are often sold bundled with other managed data services.

SAN technology standards

Various industry groups have developed standards related to SAN technology, including the Storage Networking Industry Association, which promotes the Storage Management Initiative Specification. SMI-S, as the standard is known, is intended to make it easier to manage storage devices from multiple vendors in storage area networks.

The Fiber Channel Industry Association also promotes SAN-related standards, including the Fiber Channel Physical Interface Standard, which supports 64 GFC deployments and Gen 7 solutions for the SAN market, the fastest industry-standard network protocol that enables networking. storage area up to 128 GFC. .

SAN management

A SAN presents serious management challenges. The physical network can be complex and requires constant monitoring. In addition, logical network configuration such as LUN masking, zoning, and SAN-specific features such as replication and deduplication can change and require regular attention. To keep the SAN at peak performance, SAN administrators mustconsider various best management practices.

Some of the most significant practices will use SAN monitoring and reporting. Administrators should take the time to review metrics or key performance indicators (KPIs) in several areas of the SAN:

• any KPIs related to specific storage array subsystems, such as read/write performance for each array;
• any SAN or fabric-related KPIs, such as low or no buffer credits on a SAN switch or orphaned ports as zoning changes are implemented over time;
• any KPIs related to host server I/O or workload performance, such as I/O throughput, for each virtual machine accessing the SAN; Y
• any KPIs related to SAN/LUN capacity; Look for trends or capacity shortages.

By implementing a regular review process and taking advantage of the reporting and alerting capabilities within the SAN, an administrator can ensure a clear view of the health of the SAN and take proactive steps to keep the SAN running smoothly.

Additionally, SAN management can take advantage of features and functionality designed to automate the SAN or mitigate storage outages. As examples, SANs that allow the use of policies for tasks like provisioning and data protection can help administrators avoid oversights and errors that can waste storage or compromise security. Similarly, using features like native replication can help protect valuable data while maintaining constant access to that data.

SAN remote managementit is a growing requirement for SAN management. This allows SANs to be built outside of the main data center in remote locations or for a single SAN administrator to support one or more SANs from anywhere in the world. Remote SAN management requires a reliable network connection between the management tool (the administrator) and the SAN being managed. The remote tool must be able to transmit comprehensive SAN health details such as the KPIs mentioned above, support provisioning, and initiate diagnostics to help locate and eliminate potential SAN problems. Common remote SAN tools include Storage Resource Monitor from SolarWinds, IntelliMagic Vision for SAN, and Infrastructure Monitoring from EG Innovations.

This was last updated onSeptember 2020

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