Introduction to Unified NAS & IPSAN

by Gopi

November 13, 2008 —

Introduction to Unified NAS & IPSAN in Comparison with FCSAN
Approach towards networked storage started in the 1980s with the introduction of Network Attached Storage devices and continued later in the 1990s when Fibre Channel (FC) emerged as an alternative method of connecting storage. FC could be used in either a loop technology, with up to 126 devices attached to a loop, or in a fabric with switches connecting multiple file servers and storage devices. This removed the direct connection between file servers and storage, allowing storage to be networked with multiple file servers sharing storage devices on a Storage Area Network (SAN).
Network Attached Storage:
Network storage was developed to address the challenges inherent in a server-based infrastructure such as direct-attached storage. Network-attached storage, or NAS, is a unique purpose device, comprised of both hard disks and management software, which is entirely dedicated to serve files over a network. As we are aware that, a server has the dual functions of file sharing and application serving in the DAS model, potentially causing network slowdowns. NAS relieves the server of storage and file serving responsibilities, and provides a lot more flexibility in data access by virtue of being independent. Another important consideration for a medium sized business or large enterprise is heterogeneous data sharing. With DAS, each server is running its own operating platform, so there is no common storage in an environment that may include a mix of Windows, Mac and Linux workstations. NAS systems can mix into any environment and serve files across all operating platforms. On the network, a NAS system appears like a native file server to each of its different clients. That means that files are saved on the NAS system, as well as retrieved from the NAS system, in their native file formats. NAS is also based on industry standard network protocols such as TCP/IP, FC and CIFS.

Background of IP-SAN:
A SAN is a network that connects file servers and storage devices. A SAN storage device is a block-structured storage device, serving blocks to a file server. The most important thing about a SAN is that it separates the storage from servers, allowing the storage to be utilized and managed in much more effective way than with DAS. This allows storage to be consolidated in storage pools and allocated to file servers, as needed.
Instead of a systems manager having to take a server down to deal with a failed disk or a server that has run out of space, with a storage network servers can be provided with virtual disks with built-in redundancy and the ability to grow as the demand for capacity grows. Unlike a Direct Attached environment, storage can be added to a SAN without server downtime and disruption. Separating storage from servers also enables highly available systems with no single point of failure to be developed. If a file server fails, another can easily take over its storage, and if storage is mirrored on the SAN, a file server can easily connect to a mirror of a volume if the main volume (or the path to the main volume) fails.
In a client-server environment, file servers serve files to clients using a network filing protocol such as CIFS or NFS. A NAS device is simply a specialized file server, which replaces a conventional file server. What makes NAS attractive is the advantage it offers over a conventional file server. NAS devices are appliances, and the most important feature of appliances is their ease of use. NAS appliances are sold as plug-and-play devices, which can be added to a Local Area Network and configured within a few minutes. Configuration is done using simple, user-friendly Web GUIs. When you add a new NAS device to a network, client systems will simply see a new file server with one or more new network shares available.
The major selling point for low- and mid-range NAS devices has been the fact that they provide an easy way of adding storage to a TCP/IP network. NAS has been very successful as a storage technology, and NAS products have penetrated most sectors of the storage market. At the low-end, very low cost NAS appliances have been sold to small businesses with little technical expertise; mid-range systems with extra functionality such as hardware RAID and mirroring have sold into the middle market; high-end systems with high-performance and business continuance features have been sold into the enterprise sector.

Limitations of Fibre Channel Storage Configurations:
FC does offer a solution to this by superimposing forms of access control on the storage devices. If the device is a RAID controller, the controller can check and limit access to individual RAID volumes to particular servers; this is known as LUN-masking. In a Fibre Channel Fabric, there are switches connecting the various nodes together. These switches can also be used to control access to devices, using a technique known as zoning. These techniques work but they are cumbersome to set-up, interoperability can be an issue, and the costs are typically expensive. It is often characterized by its high interconnection data rates (4Gigabits/sec) between member storage peripherals and by its highly scalable architecture.
A further issue with Fibre Channel is data security. In some computer-room environments, where physical access to the network infrastructure can be controlled, security of data is not really an issue. However, if SANs are extended over a Metropolitan Area Network (MAN) or a Wide Area Network (WAN) then protection of data from unauthorized access becomes important. Currently, the only way this can be implemented in an FC SAN is with additional, expensive and proprietary equipment.
These issues have resulted in FC SANs being an expensive and complex solution, both to install and to maintain--although recently those costs have started to reduce. In fact, a large number of installations actually use Fibre Channel as direct-attached storage, where the performance benefits can still be reaped but the benefits of pooled storage architecture are not fully realized.

Unified Storage Convergence:
NAS devices do not usually provide business continuance features, except in the expensive high-end products. Low- and mid-range NAS devices may have RAID behind them, but that is usually as far as it goes. If features such as high availability, clustering, remote mirroring or snapshot are required, these can be provided more effectively and with more scalability within a storage area network. SANs are also better when it comes to backup; with NAS, backup must be done over the LAN, whereas if a SAN is available it can be achieved by sending the data directly over the SAN. Modern backup techniques such as Third Party Copy provide a way of performing server-less and LAN-free backup over a SAN and, hence, have a minimal impact on file servers and the LAN.
NAS products suffer a number of other limitations. The first of these is that a file-based protocol is far from ideal to use with a modern high-performance database application. Microsoft has repeatedly warned about the dangers of using a NAS device as the storage for Exchange and SQLserver applications. Another limitation is the fact that NAS boxes create isolated islands of storage. These islands cannot be treated as common storage pools, and tools to manage multiple heterogeneous NAS devices from a single management tool is not technically feasible at the current time (although this may happen someday). Concepts such as provisioning additional storage from one system to another transparently is something the vendors have only just started to grapple with.
IP-based storage area networks reduce the start-up cost even further while building on a company's existing infrastructure and management skills. Ethernet-based products are ubiquitous, with a cost-per-port that is constantly been driven down by the economies of scale of the market per year.

Salient Benefits of Unified Storage:
* More flexible, scaleable systems
* Centralized management of networked storage resources using IP-based tools provide much more efficient management of those resources, requiring less dedicated staff time.
* Use of standard-based IP-SAN technology leads to significant increases in functionality, providing additional features such as remote replication, automated storage provisioning, device and storage virtualization, as well as improved backup performance.
Comparison of IP-SAN with FC SAN
Fibre Channel has not brought about the anticipated widespread adoption of SANs, and its use is restricted to more expensive higher end solutions. There remains a large, untapped market sector immediately below the FC market where the benefits of SAN are required but, so far, not exploited. SANs allow storage-related features such as snapshot and mirroring to be implemented in the SAN fabric, avoiding overhead on file servers and putting the functionality where it belongs on SAN devices such as storage controllers. The ability of the iSCSI protocol to scale to the Internet provides a standard way to implement remote mirroring of SAN storage, enabling disaster recovery plans to be implemented. Security in an IP-SAN leverages security protocols developed for the Internet, enabling data to be protected when it traverses public networks.
The benefit of SANs are that they provide flexible, high-performance and highly scalable storage environments. IP-SANs do this using the same low cost, well understood Ethernet infrastructure used by filer servers and NAS devices. This is in contrast to FC SANs, which use much more expensive and specialized components, and with them come higher management costs. This means that IP-SANs can provide a very cost-effective way of providing improved data availability, more effective storage capacity utilization and quicker and cheaper deployment of storage. These factors all result in a lower Total Cost of Ownership.
In the short term, Fibre Channel and IP-SANs will co-exist, with the advent of a number of bridging and converter products. In the end game standard-based technology using Ethernet will win out. Analysts are divided between those who think it will take ten years to those who--rather surprisingly--think it will happen three.
The benefits of SANs have, until now, been limited to larger companies willing to invest significant time and resources required to install and configure in a new infrastructure. It is clear that Storage Networking technology offers enormous benefits in terms of reduced management costs, easier maintenance and improved systems flexibility. IP-based SANs reduce the start-up cost even further while building on a company's existing infrastructure and management skills.

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