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Why Storage area networks have evolved?
• Capacity – the amount of data storage space is increasing. The historic data shows the growth of enterprise data storage has surpassed the exponential growth rate projected by Moore’s law (doubling every 18 months).
• Performance – the bandwidth for delivering storage content is growing to match the increased speed of computer processing power, the speed of data communication networks, and the speed requirement of emerging applications such as multimedia applications.
• Availability – as people and enterprises become more and more reliant on the content in the data storage, the reliability and availability of data storage systems networks must be dramatically increased to prevent the severe consequences that may result from loss of data content and loss of access to data. Mission critical storage networks are required to achieve “5-9’s “ (99.999%) availability and the capability to recover from catastrophic disasters via mirroring and backup techniques that protect the content through geographic diversity.
• Scalability – the data storage solution must not only be able to satisfy the current storage requirements, but also be easy to grow to address the increased demand of future applications.
• Cost – the cost of ownership needs to be reduced. That includes not only the cost of hardware system, but also the cost of maintaining and managing the data storage.
Driven by the above requirements, various storage-networking technologies have undergone a fairly rapid adoption to become mainstream enterprise solutions.
What is a Storage Area Network?
The Storage Network Industry Association (SNIA) defines the SAN as a network whose primary purpose is the transfer of data between computer systems and storage elements.
SAN consists of a communication infrastructure, which provides physical connections; and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust.
The term SAN is usually (but not necessarily) identified with block I/O services rather than file access services.
A SAN can also be a storage system consisting of storage elements, storage devices, computer systems, and/or appliances, plus all control software, communicating over a network.
What makes a SAN different?
What Makes a Good SAN?
A SAN must be highly available: A single SAN connecting all computers to all storage puts a lot of enterprise information accessibility eggs . The SAN had better be pretty indestructible or the enterprise could literally be out of business. A good SAN implementation will have built-in protection against just about any kind of failure imaginable
The I/O performance of a SAN must grow or scale as the number of interconnected devices grows:
If a SAN interconnects a lot of computers and a lot of storage, it had better be able to deliver the performance they all need to do their respective jobs simultaneously. A good SAN delivers both high data transfer rates and low I/O request latency. Moreover, the SAN’s performance must be able to grow as the organization’s information storage and processing needs grow. As with other enterprise networks, it just isn’t practical to replace a SAN very often.
On the positive side, a SAN that does scale provides an extra application performance boost by separating high-volume I/O traffic from client/server message traffic, giving each a path that is optimal for its characteristics and eliminating cross talk between them.
When designing a SAN to access critical enterprise data, make sure the SAN is highly available (i.e., can survive failures of both components in it and components attached to it) and make sure it can grow well beyond anticipated peak performance needs without disruption.
When evaluating SAN implementation options, once the basic capacity, availability, and performance requirements can be met, look for advanced functionality available in the chosen architecture and consider how it might be used to further reduce cost or enhance the information services delivered to users.
Architecture Of SAN
Advantages Of SAN
Better disk utilization- Better disk utilization is the primary benefit of using SAN storage. When your storage is available in a centralized manner then everything can be managed as a single entity.This gives you an advantage to slice up the different pools of storage resources at a network level and assign the storage in an intellectual manner to the available server applications.
Improves the Availability Of Application:In order to serve those applications which need high availability, a SAN solution will be the right storage medium. There are cases where applications fail due to silent data corruptions or due to some hardware/software fault. But in a storage array of a SAN, data protection algorithms are set to the peak, to ensure data consistency.
Reduce backup time- If an enterprise or a data storage environment is facing a situation where its backup is taking too long, then SAN solution needs to be deployed in these circumstances. The technology of a SAN solution is such that it can make a duplicate of a data copy within no time. Thus these duplicates can serve as a backup for your data or act as a source to backup the data to tape library.
Facilitates disaster recovery for multiple applications- If your data center/ IT environment has critical servers running on applications which cannot be let down, then there needs to be a data continuity solution in place, which can act as a failover when a disaster strikes. If this indeed is the scenario then SAN based DR solution will be the right choice. Since the volume of downtime is critical in most organizations when disaster strikes, a SAN solution will effectively reduce the downtime number to a negligible value.
Long Distance Connectivity:SANs have the advantage over all other storage connectivity for distance at 10km (about 6 miles). Not that you'll necessarily use that distance capability, but it's there if you need it. Having the advantage of distance allows you to consolidate your storage into an isolated location dedicated to storage and separate from the systems it serves.
Centralized Management
If you have SAN arrays from several different vendors because your data center has grown over the years, stress not, SAN vendors have created software management tools to manage your heterogeneous environment with ease. But, better than multiple vendor management capability, all of your SAN environments can be centrally managed from this single interface. This capability provides efficient and centralized storage management.
7. Increased Utilization
Rather than hundreds or thousands of partially utilized local disks wasting power and generating heat in your data center, you could have dozens of SAN disks have no wasted space on them. How so? Thin provisioning on the storage side (i.e., on the SAN) uses space more effectively than local storage does. As a system requires more storage, the SAN allocates it dynamically. Yes, this means that physical systems can enjoy thin provisioning just like your virtual ones do.
Bootableespite the benefit of more fully utilized disks, as highlighted in advantage No. 7, you do not need to use local disks for the server operating system. It's possible to run diskless physical servers and boot directly to the SAN for your operating system, swap space (pagefile), and all applications. That's right, just like virtual machines.
1. Scalability
SAN scalability means that you don't have the limit of a handful of disks that you can attach to a system. SANs can grow to hundreds of disks in size, whereas your server has a physical limit of about a dozen
2. Performance
SAN performance isn't affected by Ethernet traffic or local disk throughput bottlenecks. Data transmitted to and from a SAN is on its own private network partitioned off from user traffic, backup traffic and other SAN traffic.
3. Data Isolation
There's no chance of your data being copied or stolen by anyone sharing the same SAN with you. Not even the SAN admins can see your data. When correctly configured, SAN data is zoned. These zones protect your data from everyone else's on the same SAN. An example of SAN zone separation is how UNIX servers can connect to a SAN and Windows servers connect to the same SAN, but the data that each group of servers accesses is different. In effect, Windows systems can't "see" UNIX data and vice versa.
4. Uptime
There's nothing quite like a SAN to assure 100-percent storage availability. SAN systems require no reboots to add new disks, to replace disks or to configure RAID groups. The ability to stream data between SANs for data backup and recovery also increases performance by bypassing server systems completely.
5. Workload Isolation
Zoning also separates your workloads from one another on a SAN. Not only is your data protected by zoning, but it also provides a barrier against other non-related workloads from affecting your application's performance. Sharing a SAN isn't a performance problem for applications when zones are in place.
Enables Storage Virtualization:
SAN allows you to virtually centralize storage. You can use SAN to isolate physical storage devices from the virtual presentation that clients see. This separation provides a high level of flexibility in distributing and reconfiguring resources. Storage on a SAN is shared, resulting in centralized management, better utilization of disk and tape resources, and enhanced enterprise-wide data management and protection.
Drawbacks Of SAN:
1.SANs are very expensive as Fibre channel technology tends to be pricier and maintenance requires a higher degree of skill
2.Leveraging of existing technology investments tends to be much difficult. Though SAN facilitates to make use of already existing legacy storage, lack of SAN-building skills has greatly diminished deployment of homegrown SANs. So currently pre-packaged SANs based on Fibre channel technology are being used among the enterprises.
3. Management of SAN systems has proved to be a real tough one due to various reasons. Also for some, having a SAN storage facility seems to be wasteful one.
4. Also, there are a few SAN product vendors due to its very high price and very few mega enterprises need SAN set up.
5.For single applications,it is ineffective like one need disaster recovery for a single application for which software based solutions might be cost effective.
6.Replication of data for disaster recovery is common problem but which can’t afford fast WAN connections.
Applications Of SAN:
Applications that require the transfer or movement of large amounts of data are prime candidates for SAN.
These applications may refer to horizontal applications (e.g., backup, archiving, data replication, disaster protection, and data warehousing) or vertical applications (e.g., online transaction processing (OLTP), enterprise resource planning (ERP) business applications, electronic commerce, broadcasting, prepress, medical, and geophysics). SAN is also well suited to making performance and high availability more scalable and more affordable in applications such as clustering and data sharing. This article discusses two major horizontal applications, backup and data sharing, and how they interact with SAN.
Backup in a SAN Environment
One of the first applications that users want when implementing SAN is to be able to back up and protect their data through the SAN. They want to offload heavy backup traffic from the LAN, free system bandwidth for production operations, and gain the speed and security advantages of centralized management that SAN offers.
Effectively protecting data on a SAN requires a number of elements. Many of them are currently in the early stages of implementation. These items include:
• Centralized management
• Support for sharing removable-media libraries
• LAN-less and server-less backup
• Heterogeneous platform support
• Remote vaulting and mirroring
• Realtime backup
Centralized management: Ideally, a central console would manage all the logical and physical storage resources of an enterprise network. The console would automatically collect, correlate, and analyze capacity, configuration, use, and performance information on all storage resources. The logical resources monitored would include file systems, directories, files, and application-specific storage repositories. The physical resources tracked would include disks, RAID systems, tape libraries, optical jukeboxes, Fibre Channel components, Network Attached Storage (NAS), and SAN switches and hubs. Nearly every vendor offers some degree of centralized management. The leaders in this area are Veritas, Legato, Computer Associates (CA), and IBM.
Support for sharing removable-media libraries: Performing backups often involves backing up many different servers to locally attached tape drives. One benefit of SAN and NAS connectivity is the ability to share resources (e.g., a large tape library) among multiple backup servers. Shared resources enable administrators to consolidate backups into one tape library.
However, the support must extend beyond simple connectivity to a library and into management. Managing a library means managing access to the media stored within it and requires dynamic drive allocation among servers, so the server that needs a drive most at a given time can get it (e.g., when recovering a large database). Managing a library involves managing not just backup but any application that might need access to tape or optical storage.
In many cases, the ability to connect a library to multiple backup servers via the SAN will justify the expense of automation. In this environment, Hierarchical Storage Management (HSM) becomes economically desirable. Legato, Veritas, CA, and Seagate Software are the leaders in developing shared tape-library support.
LAN-less and server-less backup: Backup is evolving in three phases when it comes to data movement. Currently-the first phase-data moves from the disk, to the server it directly connects to, through the LAN, to another server that, in turn, transfers data to the tape. In the second phase, SAN lets you perform backup outside the LAN. Data moves from the disk to the server, which retransmits it through the SAN to a SAN-connected library. This setup is sometimes called LAN-less backup . In the third phase, the server initiates the backup command. Data moves directly from disk to tape through the SAN fabric without further involving the server or the LAN. This configuration is called server-less backup. Intelliguard, which Legato recently acquired, has led the development of server-less backup.
Heterogeneous platform support: Early SAN implementations are generally homogeneous. As SAN environments mature, they will become more heterogeneous. Effective SAN management software will need to be able to manage any vendor's server communicating with any vendor's storage, hosting any database, application, or file system, backing up to any tape drive or library, through any switch, hub, router, or bridge. EMC and Veritas are examples of vendors supporting heterogeneous platforms.
Remote vaulting and mirroring: The connectivity distances that Fibre Channel allows-10 to 20 km., depending on usage-make it easier to deploy remote sites for business continuance and disaster recovery purposes. Use of remote backup, remote vaulting, and remote mirroring techniques are likely to increase due to this capability. SANs can also connect to WANs to achieve additional levels of connectivity and protection. CommVault is one of the vendors offering remote vaulting capability. .
Realtime (or window-less) backup: The importance of window-less backup (also called hot backup) becomes obvious when it addresses the large volume of data in a SAN centralized backup library. Realtime backup essentially lets you back up a volume or file periodically and automatically without affecting normal system operations. The technique commonly used is called a snapshot, where you make a copy of the volume needing backup, and then back up the copy while accessing and modifying the original volume in normal operations. Network Integrity leads in development, and EMC and HDS have implemented solutions in currently available products.. Major providers of total backup solutions include ADIC, ATL, Storage Tek, Hewlett-Packard (HP), Exabyte, and Overland.
Resource and Data Sharing
In a heterogeneous environment where platforms are by definition different, the distinction between resource sharing, data copy sharing, and true data sharing must be made.
Resource sharing: A storage subsystem attached to multiple computer platforms is divided into partitions, each partition being accessible only to its owning platform or to a certain number of homogeneous platforms. The administrator can reassign storage capacity to different platforms as needs change. One of the benefits of SAN connectivity is its ability to share resources (e.g., a large tape library) among multiple backup servers. Such sharing enables administrators to consolidate backups-from many different servers to locally attached tape drives-into one tape library.
Dynamic resource sharing: All storage is available to any connected host; hosts are allocated storage as they need it. If one host needs the storage, it can use any or all the available space. If a host deletes a file, that space is available to any other host. This dynamic storage sharing operates automatically and transparently. Dynamic resource sharing means that the systems administrator doesn't have to partition the storage before storing the data.
Data copy sharing: This process involves replication of the data. Data is the same across copies at the time of copy creation, but the copies can change independently afterward. There is no assurance that they will remain identical. Data access is usually prevented during replication so the copy accurately reflects all the data at a particular time. For large amounts of data, the time needed to copy it may be important, , and the amount of storage necessary to store the copy could be very large. SAN facilitates data-copy sharing by allowing high-bandwidth connections to transfer large volumes of data.
True data sharing. If you are sharing data without making a copy, multiple computer platforms can access the same physical instance of the recorded data on a storage subsystem. This type of sharing is called true data sharing. Different levels of performance and complexity exist in implementing true data sharing: The first level is when heterogeneous platforms can access data, but only the original data owner can modify it. The second level is when multiple heterogeneous platforms can update and rewrite a data item, but only one at a time. In this case, you must use a locking mechanism to momentarily prevent a platform from updating the data. The third level is called concurrent data sharing and exists when all platforms can either read or update the data at the same time. The advantages of true data sharing are numerous. With only one copy of data, you never need to replicate the data for use elsewhere, you simplify data maintenance, and you eliminate problems due to out of sync conditions. True Data Sharing among platforms running heterogeneous operating systems requires translating to one common operating system . Examples of vendors offering implementations of true data sharing in a SAN architecture are Sequent, Mercury Computer Systems, Data Direct, Transoft and Network Disk.