SAN Benefits

From: http://www.datamation.com/storage/do-you-really-need-a-san-1.html

Now that we've shot down many misconceptions about SAN, you may be wondering if SANs are ever appropriate. They are, of course, quite important and incredibly valuable when used correctly. The strongest points of SANs come from consolidation and special types of shared storage.

Historically, customers sought out SAN solutions for consolidation. A SAN allows us to combine many filesystems into a single disk array, allowing far more efficient use of storage resources. Because SAN is block level, it is able to do this anytime that a traditional, local disk subsystem could be employed.

In many servers, and even many desktops, storage space is wasted due to the necessities of growth, planning and disk capacity granularity. If we have twenty servers each with 300GB drive arrays but each only using 80GB of that capacity, we have large waste. With a SAN would could consolidate to just 1.6TB, plus a small amount necessary for overhead, and spend far less on physical disks than if each server was maintaining its own storage.

Once we begin consolidating storage, we begin to look for advanced consolidation opportunities. Having consolidated many server filesytems onto a single SAN, we have the chance, if our SAN implementation supports it, to deduplicate and compress that data which, in many cases, can result in significant utilization reduction. So the 1.6TB in our example above might actually end up being only 800GB or less. Suddenly, our consolidation numbers are getting better and better.

To efficiently leverage consolidation, it is necessary to have scale. And this is where SANs really shine — when the number of attaching nodes becomes very large. SANs are best suited to large scale storage consolidation. This is their sweet spot and what makes them nearly ubiquitous in large enterprises and very rare in small ones.

SANs are also very important for certain types of clustering and shared storage that requires single shared filesystem access. This is actually a pretty rare need outside of one special circumstance — databases. Most applications are happy to utilize any type of storage provided to them, but databases often require low-level block access to be able to properly manipulate their data most effectively. Because of this, they can rarely be used, or used effectively, on NAS or file servers. Providing high availability storage environments for database clusters has long been a key use case of SAN storage.

Outside of these two primary use cases, which justify the vast majority of SAN installations, SAN also provides for high levels of storage flexibility. Potentially, SANs can make it very simple to move, grow and modify storage in a large environment without needing to deal with physical moves or complicated procurement and provisioning. Again, like consolidation, this is an artifact of large scale.

In very large environments, SAN can also provide a point a demarcation between storage and system engineering teams, allowing there to be a handoff at the network layer, generally of fibre channel or iSCSI. This clear separation of duties can be critical in allowing for teams to be highly segregated in companies that want highly discrete storage, network and systems teams. This allows the storage team to do nothing but focus on storage, and the systems team to do nothing but focus on the systems without any need for knowledge of the other team's implementations.

For a long time, SANs also presented themselves as a convenient means to improve storage performance. This is not an intrinsic component of SAN, but an outgrowth of their common use for consolidation. Similar to virtualization when used as consolidation, shared SANs will have a natural advantage of having better utilization of available spindles, centralized caches and bigger hardware than the equivalent storage spread out among many individual servers. Like shared CPU resources, when the SAN is not receiving requests from multiple clients, it has the ability to dedicate all of its capacity to serving the requests of a single client. That provides an average performance potentially far higher than what an individual server would be able to affordably achieve on its own.

Using SANs for performance is rapidly fading from favor, however, because of the advent of SSD storage. SSDs with incredibly low latency and high IOPS performance are dropping in price to the point where they are being added to stand alone servers as local cache or potentially even being used as mainline storage. As a result, the bottleneck of the SAN's networking becomes a larger and larger factor, making it increasingly difficult for the consolidation benefits of a SAN to offset the performance benefits of local SSDs. SSDs are potentially very disruptive for the shared storage market as they bring the performance advantage back towards local storage — just the latest in the ebb and flow of storage architecture design.

Do You Need a SAN?

The most important aspect of SAN usage to remember is that SAN should not be a default starting point in storage planning. It is one of many technology choices and one that often does not fit the bill as intended — or does so but at an unnecessarily high price point either in monetary or complexity terms.

Instead, start by defining your business goals and needs. Select SAN when it solves those needs most effectively, but keep an open mind and consider the overall storage needs of the environment.

***********************another article: Why do people purchase SAN over DAS?**********************

From:  http://sqlmag.com/blog/why-do-people-purchase-san-over-das

Answer: This is actually a question that I get a lot when talking to people about moving from DAS to a SAN platform. The short answer is manageability and better utilization of disk resources. What that really means is that when you use a SAN overall manageability of the storage environment becomes much easier as you can manage the entire storage environment from a single console. This allows for not only centralized management but monitoring as well.  With a SAN platform you can see quickly and easily where your storage performance problems are which allows you to easily move resources from one server to another to increase performance where needed.

Related: SANs: Always Better Than DAS?

You get better utilization of disk resources with SAN than you do with DAS because when working with SAN the spindles aren't dedicated to a specific server. With DAS what ever server the disks are plugged into is the server that those spindles are going to be used for. If you needed 1TB of space, but had 3TB of space attached to the server, you can't allocate that 2TB of space to other servers. With a SAN platform you take the 3TB of space and carve up the space and allocate it to servers as needed. This makes adding more space to servers much easier as well. Most DAS platforms don't give you an easy way to add disk space to a single volume (or drive letter). With DAS when you need to add more disk space you need to create another disk and configure the application (or database in our case) to use that new disk.  In a SAN platform you can simply tell the SAN to add additional space to the end of the disk.  Then tell Windows that the disk is bigger and Windows will see the disk is bigger and the new space will be available.

Related: What are the benefits and issues with booting SQL Servers from the SAN?

Another utilization performance bonus that you get with SAN over DAS is that if you have applications which only use the disks at night and other applications which only use the disks during the day you can put these on the same physical disks for maximum utilization. This will allow you to have all the performance that you need for both applications without having to purchase double the disks. With DAS the only real way to do this would be to host both of those applications on the same physical server which would work, except that you no longer have any maintenance window for that server.

Beyond these two huge points there are a number of other things that SAN platforms can do that DAS simply can't. The most popular of these that people use is the ability to take snapshots and/or clones of LUNs. By using snapshots you can easily do things like offload the bulk of your DBCC CHECKDB commands to another server. You can also minimize the amount of space needed for down-level environments like Dev, QA and Staging which may need full data sets, but you don't have the budget for a full sized Dev, QA and staging platforms.

Assume for a moment that you have a 1TB database that you need to duplicate in your Dev, QA and Staging environments and you need to be able to refresh these databases on a monthly bases from production. With DAS you would need to backup and restore the 1TB database  to each of the three other platforms. This requires purchasing 4TB of space, 1TB of space for each environment. By using snapshots on a SAN instead you could snapshot the production LUNs and then present these snapshots to the Dev, QA and Staging platforms. At this point the only space used by the Dev, QA and Staging platforms will only be what ever data is changed in these platforms. Typically this would only be a small amount of data. On a 1TB database the amount of data which changes in Dev, QA and Staging would probably be around 10 Gigs per month. So added up the four platforms would now only require about 1.03TB of space (1TB for Production and about 10 Gigs for each of the other environments).

Yet another benefit that SAN storage gives you over DAS is the ability to quickly and easily change the RAID level which is used under the LUN. In a DAS to change the RAID level you'll need to delete the disk, rebuild the RAID array with the new RAID level then restore the data.  On a SAN platform you can simple configure other disks in the needed RAID level then move the LUN from the old RAID set to the new RAID set. With DAS this would be a multi-hour down time to do this. With a SAN platform this can all be done with no outage to the system, and only a minimal performance hit to the performance of the system while the data is being moved to the new RAID set. (This ability will depend on your SAN platform as some SAN platforms require that you use only a specific RAID level instead of being able to select the RAID level that you want to use, so check with your SAN vendor to see if you have this option or not.)

Hopefully this helps answer why you have, or may want to have a SAN platform in your environment.

***********************another article********************

From: http://www.conjungo.com/technology/storage-area-network/benefits-of-a-storage-area-network

• A storage area network can be easier to manage than other storage systems. By consolidating information into one easily accessible place, it becomes easier to access information while also making it simple to increase capacity as and when required.

• Automation of routine tasks. Routine tasks such as a backup can be automated so that administrators do not have to schedule their own time in order to make sure that backups are completed.

• Increased efficiency. Organisations with a number of locations and data storage locations can maximise the storage according to who needs it rather than where the information is stored. This means that storage can be used more efficiently as resources can be allocated where they are need most. The information can be made to appear as if it is in one, single repositry.

• Storage can be increased easily. It is possible to increase storage without it impacting an organisation’s network performance. Often, upgrades can interfere with the network performance or even lead to an element of down-time meaning that upgrades need to be conducted late at night or at weekends.

• Better performance. Storage devices are purely dedicated to storing information, leaving the servers within a network to be used solely to process information and applications.

• Speed of access. Storage area networks are specifically designed for one purpose – to provide storage and fast access to this data. As a result, SANs are far faster than typical servers and storage facilities. It is not necessary to purchase a server with a SAN because they are a stand-alone system, so this once again potentially reduces the cost.

• Data can be passed from one source of storage, e.g. disk and tape, across to a SAN directly rather than across a network. This means that less data is sent across the network and is therefore a more efficient way of using the servers or a network’s computing power.

• Maintenance. Because SAN work independently of the organisation’s servers, it means that if there are server issues or if maintenance is being carried out on the server(s), personnel can still access critical data on the SAN, and independently of the network, i.e. any work carried out will not impact the users of the network.

• Availability. Because data can be replicated easily, should one server or element of storage fail, the data will still be available to users. This increases the resilience of the network and is especially important in computing environments where data is viewed as mission critical.

• Better manageability. Because the storage area network can be ‘seen’ easily, it becomes much easier to manage because other storage systems are hidden by the servers thereby making the visibility of data difficult. This is not the case with a SAN.

• Management tools.  Monitoring tools can automatically find and fix any faults without the need for specialist technical personnel to be involved. Some can even alert the support department that there is a problem. Many systems are even able to remove duplicate information, e.g. a number of copies of the same word document. These duplicates can takes up a large amount of storage and as a result can have an expensive overhead.

• A storage area network can be managed from anywhere using the internet browser. So even if someone is not near the location of a SAN and some work needs to be carried out, as long as they have access to the internet they can make the necessary changes.

• A SAN can include both disk and tape so it maximises existing technologies and assets. Tapes are often used for backup because they are relatively inexpensive compared to other media. A SAN can also use other technologies including optical jukeboxes, tape libraries, and disk arrays

• A storage area network can be accessed by different computing environments or operating systems. This means that Mac users and devices operating Linux can still access the full functionality of a SAN.

• Disaster recovery. All important or critical information stored on an organisation’s computer system can be copied in real-time to another storage system located at another building. This ensures that if there are any major problems, e.g. fire, flood, users can still access information (albeit at another companies premises), within minutes rather than hours or perhaps days.

• A storage area network can be used in conjunction with Network Attached Storage. Because a SAN can communicate with a wide variety of storage devices including a NAS, it is extremely flexible and makes the most of existing infrastructure.