In this article, we are examining the third question asked in our original article The Beginners Guide to what to know before you shop for a Storage Appliance. That question in a nutshell is “How do I intend to connect my storage so that all of my applications can get to it?” Well, that question begs a good look at your current environment. Based on what you find, we will determine if you should connect to your existing environment or connect through other dedicated technologies within your existing environment. There are also other less common methods to connect to your storage.
Using Existing network infrastructure
Is your network stable? Every network administrator or sysadmin knows who the problem children are in their network. Do you have any segments or switches in your environment that are currently congested or causing delays now? Adding storage to it will only exacerbate the problem. On the flip side of that coin, a well-running network makes adding storage easy and inexpensive.
In addition, the speed of your existing network will come into play. Depending on your current storage needs, I would recommend that no one attach storage at speeds of less than 1 Gigabit Ethernet. As 10 GigE becomes more affordable and more pervasive in networks, it is never a bad idea to increase bandwidth to your storage. Fortunately, many manufacturers enable upgrading with field replaceable units. Speak with the vendor about this ability in the units you are investigating.
Most storage appliances will support a variety of connection protocols. For storage area networks (SAN), it is important that iSCSI be supported in the unit. iSCSI will support most of the externally mounted volumes or LUNs (Logical Unit Number). For Network Attached Storage (NAS), NFS is a popular way of attaching storage for most virtualization shared storage and *nix computing. These storage protocols may all be supported, or only some of them. SMB/CIFS should be supported for full functionality in a Microsoft network.
Using Dedicated connection technologies
There are situations where the use of the existing network may not be advisable. If the network is older or slow, putting the data needs of shared storage on the network will just exacerbate an already slow situation. In this case, there are dedicated connection technologies that may come to the rescue.
Ethernet connectivity is still a very viable alternative, using dedicated switches and VLANs. VLANs are Virtual Local Area Networks that allow for the logical partitioning of ports within a switch to create virtual switches and LANs. This lets you segregate data traffic and dedicate resources to the various ports that may be passing your data traffic.
Fiber Channel (FC) is a mature, well established connection technology. FC uses glass fibers to connect physical servers to physical storage using light. While this technology is a bit more expensive than traditional ethernet switches it does have advantages over ethernet. There is tremendous support for this protocol in software and hardware because it is a very stable protocol developed specifically for storage. Fiber Channel allows for data to be consistently delivered with very low overhead. Fiber Channel switches are available to connect servers to storage in a logical mesh setup, but it is also a regular practice to directly connect servers with FC Host Bus Adapters (HBA’s – think of an HBA as a fiber channel version of a network card). This will cut out the expense of a Fiber Channel switch for smaller deployments.
Exotic Connection methods
In addition to the well established protocols of Fiber Channel and iSCSI, there are other ways to connect storage. There are storage appliances out there that will allow connection to servers via specialized technologies like InfiniBand, or SAS ports. There is eSATA that is available. These various ways to connect range from the super fast (InfiniBand – and expensive by the way) to the fairly common and slow. “Exotic” connection technologies serve special cases and are outside the scope of this article. These connection technologies will limit your field of vendors, but not disqualify you from a storage appliance.
Considerations of Connectivity
In addition to the connection methods discussed above, there are also other connectivity possibilities to consider. Bonded connections is one. Bonded connections make multiple physical paths (read cables or ports) to appear as one logical path to data. In essence, two 1GB Ethernet connections becomes one logical 2 GB Ethernet connection. A single path of bandwidth to the storage appliance will be quickly overwhelmed. There will be many servers and users trying to connect to the storage. Bonding allows several ports to simultaneously send out data. Bonding also helps with failover.
Another consideration of connectivity is failover. Although it may not happen often, if a cable, NIC, or port fails on the storage appliance or on the connectivity side, all servers using that storage are suddenly unable to access data. Or all of your virtual machines may come down at once. You have placed all of your proverbial eggs in that one proverbial basket. Failover mitigates this risk accordingly.
This is often accomplished through the use of different controllers or “heads”. Two (or more) controllers allows for multiple disparate paths to the data. It allows for one head to crash and you still have access to your data. It allows for one power supply to fail, and you still have access to your data. Many manufacturers will vary on how they support this functionality, so it is important to research this carefully. Make sure that the storage appliance will run on one power supply. Verify that the controller heads support failover. Implement bonded connections.
In this article, we have discussed the final question raised in our original article about finding the best storage appliance for your environment. We have gone over considerations of attaching the shared storage to your existing network, the prospect of attaching the NAS or SAN via new connectivity, or even attaching via a special, non-standard or exotic connectivity mode. Many vendors support these differing connectivity methods. Specialized connectivity will limit the number of storage appliances that you have to choose from. Most users know that they are required from the start and can plan accordingly.