A storage area network (SAN) is any high-performance network whose primary purpose is to enable storage devices to communicate with computer systems and with each other. With a SAN, the concept of a single host computer that owns data or storage isn’t meaningful. A SAN moves storage resources off the common user network and reorganizes them into an independent, high-performance network. This allows each server to access shared storage as if it were a drive directly attached to the server. When a host wants to access a storage device on the SAN, it sends out a block-based access request for the storage device.
A storage-area network is typically assembled using three principle components: cabling, host bus adapters (HBAs) and switches. Each switch and storage system on the SAN must be interconnected and the physical interconnections must support bandwidth levels that can adequately handle peak data activities.
A good provides the following functionality to the business.
Highly availability: A single SAN connecting all computers to all storage puts a lot of enterprise information accessibility eggs into one basket. 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. As we will see in later chapters, this means that not only must the links and switches composing the SAN infrastructure be able to survive component failures, but the storage devices, their interfaces to the SAN, and the computers themselves must all have built-in strategies for surviving and recovering from failures as well.
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.
The investment required to implement a SAN is high, both in terms of direct capital cost and in terms of the time and energy required to learn the technology and to design, deploy, tune, and manage the SAN. Any well-managed enterprise will do a cost-benefit analysis before deciding to implement storage networking. The results of such an analysis will almost certainly indicate that the biggest payback comes from using a SAN to connect the enterprise’s most important data to the computers that run its most critical applications.
But its most critical data is the data an enterprise can least afford to be without. Together, the natural desire for maximum return on investment and the criticality of operational data lead to Rule 1 of storage networking.
A great SAN provides additional business benefits plus additional features depending on products and manufacturer. The features of storage networking, such as universal connectivity, high availability, high performance, and advanced function, and the benefits of storage networking that support larger organizational goals, such as reduced cost and improved quality of service.
- SAN connectivity enables the grouping of computers into cooperative clusters that can recover quickly from equipment or application failures and allow data processing to continue 24 hours a day, every day of the year.
- With long-distance storage networking, 24 × 7 access to important data can be extended across metropolitan areas and indeed, with some implementations, around the world. Not only does this help protect access to information against disasters; it can also keep primary data close to where it’s used on a round-the-clock basis.
- SANs remove high-intensity I/O traffic from the LAN used to service clients. This can sharply reduce the occurrence of unpredictable, long application response times, enabling new applications to be implemented or allowing existing distributed applications to evolve in ways that would not be possible if the LAN were also carting I/O traffic.
- A dedicated backup server on a SAN can make more frequent backups possible because it reduces the impact of backup on application servers to almost nothing. More frequent backups means more up-to-date restores that require less time to execute.
Replication and disaster recovery
With so much data stored on a SAN, your client will likely want you to build disaster recovery into the system. SANs can be set up to automatically mirror data to another site, which could be a fail safe SAN a few meters away or a disaster recovery (DR) site hundreds or thousands of miles away.
If your client wants to build mirroring into the storage area network design, one of the first considerations is whether to replicate synchronously or asynchronously. Synchronous mirroring means that as data is written to the primary SAN, each change is sent to the secondary and must be acknowledged before the next write can happen.
The alternative is to asynchronously mirror changes to the secondary site. You can configure this replication to happen as quickly as every second, or every few minutes or hours, Schulz said. While this means that your client could permanently lose some data, if the primary SAN goes down before it has a chance to copy its data to the secondary, your client should make calculations based on its recovery point objective (RPO) to determine how often it needs to mirror.
With several servers able to share the same physical hardware, it should be no surprise that security plays an important role in a storage area network design. Your client will want to know that servers can only access data if they’re specifically allowed to. If your client is using iSCSI, which runs on a standard Ethernet network, it’s also crucial to make sure outside parties won’t be able to hack into the network and have raw access to the SAN.
Capacity and scalability
A good storage area network design should not only accommodate your client’s current storage needs, but it should also be scalable so that your client can upgrade the SAN as needed throughout the expected lifespan of the system. Because a SAN’s switch connects storage devices on one side and servers on the other, its number of ports can affect both storage capacity and speed, Schulz said. By allowing enough ports to support multiple, simultaneous connections to each server, switches can multiply the bandwidth to servers. On the storage device side, you should make sure you have enough ports for redundant connections to existing storage units, as well as units your client may want to add later.
Uptime and availability
Because several servers will rely on a SAN for all of their data, it’s important to make the system very reliable and eliminate any single points of failure. Most SAN hardware vendors offer redundancy within each unit — like dual power supplies, internal controllers and emergency batteries — but you should make sure that redundancy extends all the way to the server. Availability and redundancy can be extended to multiple systems and cross datacentre which comes with cost benefit analysis and specific business requirement. If your business drives to you to have zero downtime policy then data should be replicated to a disaster recovery sites using identical SAN as production. Then use appropriate software to manage those replicated SAN.
Software and Hardware Capability
A great SAN management software deliver all the capabilities of SAN hardware to the devices connected to the SAN. It’s very reasonable to expect to share a SAN-attached tape drive among several servers because tape drives are expensive and they’re only actually in use while back-ups are occurring. If a tape drive is connected to computers through a SAN, different computers could use it at different times. All the computers get backed up. The tape drive investment is used efficiently, and capital expenditure stays low.
A SAN provide fully redundant, high performance and highly available hardware, software for application and business data to compute resources. Intelligent storage also provide data movement capabilities between devices.
Best OR Cheap
No vendor has ever developed all the components required to build a complete SAN but most vendors are engaged in partnerships to qualify and offer complete SANs consisting of the partner’s products.
Best-in-class SAN provides totally different performance and attributes to business. A cheap SAN would provide a SAN using existing Ethernet network however you should ask yourself following questions and find answers to determine what you need? Best or cheap?
- Has this SAN capable of delivering business benefits?
- Has this SAN capable of managing your corporate workloads?
- Are you getting correct I/O for your workloads?
- Are you getting correct performance matrix for your application, file systems and virtual infrastructure?
- Are you getting value for money?
- Do you have a growth potential?
- Would your next data migration and software upgrade be seamless?
- Is this SAN a heterogeneous solutions for you?
Storage as a Service vs on-premises
There are many vendors who provides storage as a service with lucrative pricing model. However you should consider the following before choosing storage as a service.
- Does this vendor a partner of recognised storage manufacturer?
- Does this vendor have certified and experienced engineering team to look after your data?
- Does this vendor provide 24x7x365 support?
- Does this vendor provide true storage tiering?
- What is geographic distance between storage as a service provider’s data center and your infrastructure and how much WAN connectivity would cost you?
- What would be storage latency and I/O?
- Are you buying one off capacity or long term corporate storage solution?
If answers of these questions favour your business then I would recommend you buy storage as a service otherwise on premises is best for you.
NAS OR FC SAN OR iSCSI SAN OR Unified Storage
A NAS device provides file access to clients to which it connects using file access protocols (primarily CIFS and NFS) transported on Ethernet and TCP/IP.
A FC SAN device is a block-access (i.e. it is a disk or it emulates one or more disks) that connects to its clients using Fibre Channel and a block data access protocol such as SCSI.
An iSCSI, which stands for Internet Small Computer System Interface, works on top of the Transport Control Protocol (TCP) and allows the SCSI command to be sent end-to-end over local-area networks (LANs), wide-area networks (WANs) or the Internet.
You have to know your business before you can answer the question NAS/FC SAN/iSCSI SAN or Unified? Would you like to maximise your benefits from same investment well you know the answer you are looking for unified storage solutions like NetApp or EMC ISILON. If you are looking for enterprise class high performance storage, isolate your Ethernet from storage traffic, reduce backup time, minimise RPO and RTO then FC SAN is best for you example EMC VNX and NetApp OnCommand Cluster. If your intention is to use existing Ethernet and have a shared storage then you are looking for iSCSI SAN example Nimble storage or Dell SC series storage. But having said that you also needs to consider your structured corporate data, unstructured corporate data and application performance before making a judgement call.
Decision Making Process
Let’s make a decision matrix as follows. Just fill the blanks and see the outcome.
|Workloads||I/O||Capacity Requirement (in TB)||Storage Protocol
(FC, iSCSI, NFS, CIFS)
|Option||Rating Requirement (1=high 3=Medium 5=low )|
|Risk Type||Rating (Low, Medium, High)|
|Loss of productivity|
|Loss of redundancy|
|Limited upgrade capacity|
|Disruptive migration path|
Service Data – SLA
|Service Type||SLA Target|
Rate storage via Gartner Magic Quadrant. Gartner magic quadrant leaders are (as of October 2015):
- Nimble Storage
To make your decision easy select a storage that enables you to cost effective way manage large and rapidly growing data. A storage that is built for agility, simplicity and provide both tiered storage approach for specialized needs and the ability to unify all digital contents into a single high performance and highly scalable shared pool of storage. A storage that accelerate productivity and reduce capital and operational expenditures, while seamlessly scaling storage with the growth of mission critical data.