ITEM: GbE VS FC in the SAN ?
techweb.com
<<SANs are designed specifically to link external storage devices directly to a net without going through a computer server. Much of the basics of what these SANs will look and feel like-whether they will be based on Fibre Channel or Gigabit Ethernet links, Unix or Windows NT operating systems-is still being debated.>>
<<Some observers feel that Gigabit Ethernet will be the most popular approach for networked storage, leveraging the huge installed base of Ethernet networks. Others say that Fibre Channel will dominate because it was designed in large part for storage. Still others are looking at ways to blend the two.
"There may be a sizable investment to switch from a network applications to Fibre Channel," Berry said. "Customers might not make that Fibre Channel investment if they can move up to Gigabit Ethernet. We believe Fibre Channel will play a big part in this, but the two are different in some respects."
According to some observers, Ethernet holds a solid advantage since information technology managers in major corporations are very familiar with it and have little knowledge of Fibre Channel. But those who understand Fibre Channel note that it has far more benefits than Ethernet.
"Fibre Channel is a huge enabler," said Bob Wilson, senior marketing vice president at Intelliguard Software Inc. (Dublin, Calif.), which creates network storage software. "We are now demonstrating a Fibre Channel backup product that essentially provides backup from disk to tape without going through the server, so it frees up a lot of resources, particularly network bandwidth," said Wilson.>>
<<Fibre Channel proponents say that their architecture was designed for this type of application, contending that this approach will provide an edge over Gigabit Ethernet.
"An interesting thing about Fibre Channel is that it's a chameleon," said Dal Allan, president of ENDL Consulting (Saratoga, Calif.). "If you want it to be SCSI, it will behave like SCSI. If you want to run Internet Protocols , it looks like IP over Internet. That's why you can mix and match IP and SCSI; it doesn't matter over Fibre Channel."
But Fibre Channel has its weaknesses. Since both it and the concept of networked storage are very new, there are still problems to be ironed out.
Among them is that the so-called Class 3 commands used in Fibre Channel don't work well with tape drives. "Class 3 works well with disk drives, but it doesn't work very well with tape," said Thompson. "Class 3 is unacknowledged, so when you send a frame to a device it will begin working on it. If it doesn't get it, it will take a time out. That's okay with disk drives, because the time outs are pretty short. But when you're sending commands to a tape drive, the time out to wait until you know if it arrived can be very long, since you have to wait the longest time that's possible. When you're dealing with a tape drive that might have to stop and rewind the tape, that can be a pretty long wait."
That is compounded by incompatibility issues within Fibre Channel. "If you replace one hub with another, there's no guarantee the system will still work," Wilson said. "Also, Fibre Channel has no concept for device locking or sharing, which is a problem when every server on the network accesses every storage device. Nothing prevents Server 1 from loading a tape cartridge to read it and Server 2 ejecting it to load another.
Another obstacle that will face these system implementations is the use of disparate operating systems. Windows NT and Unix are both widely used in major corporations, so integrators will have to figure out ways to let such products work together while maintaining some level of independence.
One central issue in this portion of the design challenge is to minimize the chance that one system will alter data for the other. Another is that one segment will consume too much space, leaving little for the other approach. Designers have already come up with some solutions for these challenges.
"We are now demonstrating a heterogeneous environment that allows SAN to be separated into NT environments and Unix environments and doesn't let one server try to get at disk space being used by another," said Peter Tarrant, vice president of business development at Brocade Communication Systems Inc. (Irvine, Calif.).>>
<<Tarrant of Brocade added that "end users in data centers have major problems designing servers and centralized storage and at the same time providing a good backup environment to back up or restore mission critical data. What we see is that Fibre Channel technology switches particularly provide an infrastructure that lets you add storage and backup. Probably one of the leading needs is to be able to reliably back up data and restore it."
Though the push to attach these peripherals directly to networks is seen as a hot new movement today, that's not totally true. As with many concepts, storage-oriented networks are a fairly old concept that is being revised to work in the open environments of today's computer systems.
"SAN existed before, but it's always been proprietary," said Allan of ENDL Consulting. "Now we're headed to interoperability, though it's not totally heterogeneous now."
Not surprisingly, there's plenty of effort to complete this transition to truly open systems. How quickly it will occur is still a question since many different parties must get involved, and some segments in the industry are working at a faster pace than others.>> |
