FC SANs: Not For SMBs
For the purposes of this article, we'll use our own definition: If you have a non-technology business with fewer than 20 people on your IT staff, then you are too small for a Fibre Channel SAN except in some very specialized cases.
Today's NAS products provide integrated solutions with good performance that are significantly more cost-effective than the real cost of Fibre Channel networks. There are few very good reasons to have a Fibre Channel network for an SMB. Fibre Channel offers significant performance advantages over NAS environments, but do you need that performance? Fibre Channel also offers some significant advantages for managing large amounts of data, and vendors have made strides developing Fibre Channel solutions for SMBs, but I think that most small and medium business should not be looking at Fibre Channel, and here's why.
We'll start with the costs of Fibre Channel, which break down into two areas: Fibre Channel hardware and personnel costs associated with the hardware, and software costs needed to make use of the hardware.
Not that long ago, Fibre Channel HBAs cost almost $2,500 per port, and director-class Fibre Channel switches cost almost $1,000 per port. Director-class switches are switches that provide hot swapping, dual power supplies, hot rebooting and a number of other features required for high reliability environments.
Today the cost of both Fibre Channel HBAs and Fibre Channel switch ports for both director and non-director class switches have dropped dramatically, but Gigabit Ethernet ports for both switches and Gigabit NICs are still significantly cheaper. iSCSI host connections are also cheaper than Fibre Channel HBAs. All in all, the cost of a Fibre Channel network is far more expensive per port than Gigabit Ethernet, and one of the advantages of Gigabit Ethernet is that it can support multiple uses for both TCP/IP network traffic and encapsulated TCP/IP in other protocols for data.
The cost of Fibre Channel is not just the cost of the hardware. In small and medium businesses, the cost of consulting, training, downtime and configuration and a host of other costs is often far more costly than just the $5,000 to $10,000 for hardware and software.
The question many people ask today is whether managing a Fibre Channel network is really that difficult. In my opinion, it is becoming easier than it used to be and is really not that difficult, but it can still be cumbersome, and it is quite different than managing TCP/IP networks. For a small business, different can be expensive, since it can cost time and time equals money.
If you buy a Fibre Channel network, you may need other types of software to manage, configure and use the environment. Obviously, you'll need the same type of management software you use for your current TCP/IP based network. In addition to that, you might need a specialized file system.
If you need less than 20 terabytes of storage, today's free file systems will likely meet your performance needs, but what about disaster recovery issues? Will you have to buy backup software to manage the file system and tape drives for your backups? Even small business cannot skip disaster recovery planning, and just having a mirror on site does not address Katrina-like disasters. If you buy a NAS product with integrated backup, you usually don't have to think about backup policy and procedures, at least with the higher-end NAS devices, because backup and suggested procedures are often included in the cost of many NAS products.
So you might need to consider purchasing a file system. This is not as much of a requirement as it might have been five or 10 years ago, since file systems with reasonable performance for smaller systems come standard with most systems today, whether it is IBM, HP, Sun or some other vendor. Of course, you get a free file system with Windows and a myriad of file systems with Linux. Still, there are vendors selling file systems, and SMBs might be tempted to consider them even though almost no one with configurations under 10TB really needs to consider buying a file system.
In most of the environments I work in — measured in gigabytes per second and hundreds of terabytes — performance is a critical issue. These requirements are not the requirements for SMBs, however. SMB performance requirements are much smaller and can usually be handled with NAS systems.
With most NAS systems you are up and running in a few hours at most, and NAS can meet most of the performance needs of most SMBs. Most of the upper-tier NAS devices will support up to 200 MB/sec full duplex for the larger configurations, while the lower-tier boxes will support in the 50 MB/sec to 100 MB/sec rate half duplex, with the mid-tier products somewhere in between. A single 2 Gb Fibre Channel RAID controller can support up to 200 MB/sec full duplex, but most controllers except for high and mid-range controllers support far less. Large enterprise controllers do not provide streaming performance, but support I/Os per second.
Fibre Channel SANs have two significant performance advantages over NAS:
- Latency is far lower for Fibre Channel SANs than for NAS devices, given the multiple protocols and the distance between the NAS server and client and hardware and software overhead; and
- Generally, CPU overhead for NAS devices is high, since all data must be moved over TCP/IP, which causes significant CPU overhead. This could change, however, with the introduction of TOE cards for NAS clients.
Like it or not, failover with SANs is just plain hard. If you have multiple RAID controllers, you need to determine if the controllers are active/active (all controllers can read and/or write to all LUNs) or active/passive (a controller owns a LUN and the other controller can see it, but the path from the other controller is not used unless the primary controller path fails). Given the issues with controller types, different drivers for different machines and operating systems, and issues with different Fibre Channel switches, failover is not simple. Failover for TCP/IP networks is generally consistent, and most sites have far more domain knowledge about how to do it, and good standards exist and have for a long time.
I am sure that the Fibre Channel vendor community will take issue with the premise that Fibre Channel SANs should not be adopted by most SMBs, but from my perspective, the only big advantages Fibre Channel SANs have are performance, especially for IOPs considering the latency, and scalability, since most Fibre Channel SANs can support file systems that can be more than 32 terabytes. If you have those requirements and are a small business, the choice is clear: go with a Fibre Channel SAN. The tradeoff is simplicity verses scalability. If you are a small business with these requirements, you need to have the staff and training to achieve your business objectives. Once again, it is all about understanding your requirements. This is true for any technology.
Henry Newman, a regular Enterprise Storage Forum contributor, is an industry consultant with 25 years experience in high-performance computing and storage.
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