New directions for switches


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Rule No. 1: Test, test and test some more. Unless it's a one-vendor system, every storage environment is different. Vendors can certify their products with major storage products, but they can't possibly check every possible configuration with a storage area network (SAN). In other words, you're responsible for determining if a vendor's Fibre Channel (FC) switch works as advertised.
McData Corp., Broomfield, CO, continues to advertise that its directors support five-nines of availability. Yet some field engineers report that the McData directors they support lock up under certain conditions.
Brocade Communications Systems, in San Jose, CA, hasn't escaped user dissatisfaction either. Some users complain about the number of inter-switch links (ISLs) required to tie together multiple Brocade departmental switches, the time required to perform firmware upgrades on multiple switches and they also express concern about what they perceive as Brocade's initial failings in the high end of the market. Nancy Marrone-Hurley, a senior analyst at the Enterprise Storage Group, in Milford, MA, goes so far as to say that unless Brocade responds at the high end of the FC market, the high-end market will be dominated by McData and Cisco.
Computer Network Technology Corp. (CNT), Minneapolis, MN, appears to be a mystery wrapped up in an enigma to end users. Users at a breakout session at the Storage Decisions conference in Chicago rated it as fourth among switch vendors and considered Cisco a more acceptable choice.
Inrange Technologies, Lumberton, NJ. Former employees of Inrange say that part of the reason they left Inrange is that they believe the company wasn't delivering on the software feature functionality that they internally were told existed in the product. They found out after they sold the product the functionality wasn't there.
The bottom line is that all of the switch vendors have some skeletons in their closets. It's premature to look to any one FC switch vendor to provide all of the answers or expect their existing product line to work flawlessly in every environment. For now, users should view current purchases as more tactical than strategic.

Security, storage and transport services are establishing residence within the fabric either as standalone appliances or in the switch. Hardware and software vendors with no previous presence in the network hope to establish their service as the default solution in the fabric.

As these interlopers move in, how do the dominant Fibre Channel (FC) switch vendors respond? And more importantly, how do their new switches fit into your storage environment? 2003 was the year of acquisitions and alliances for switch vendors as they fought to gain a technical advantage against their competitors. McData Corp., in Broomfield, CO, bought Sanera Systems Inc. and Nishan Systems; Brocade Communications Systems Inc., based in San Jose, CA, purchased Rhapsody Networks and Cisco Systems took over Andiamo Systems. Meanwhile, EMC Corp. and Veritas Corp. announced that they will form strategic alliances with Cisco and Brocade to port their storage management software to the fabric, but provided little details on when and how.

Most importantly, how should users respond to all of these announcements? One approach is to throw caution to the wind and begin deploying these new fabric technologies. The more cautious approach in selecting a new switch is to rely on more traditional FC measurements of port count, interoperability, reliability and high availability when making a selection, ignoring, at least for the moment, the hoopla surrounding these dramatic changes being brought to the FC fabric.

For now, storage area network (SAN) admins looking to upgrade switches need to check out new FC transport services such as 4Gb and 10Gb FC speeds, virtual SANs (VSANs) and hard partitioning. They also need to pressure vendors for better solutions to their inter-switch link (ISL) issues. Security administrators should evaluate the new security risks that FC switches introduce into the organization; storage admins should start to weigh in on fabric-based virtualization, volume management and other storage services beginning to appear in the fabric.

FC transport services
If you're only looking at switches for transport services, 1Gb and 2Gb FC continues to be a mainstay for connecting servers to storage. FC switches and directors provide a highly available, scalable and reliable method for block I/O storage networking connectivity. (For more information, see "Switch selection criteria"). Furthermore, these devices offer a growing diversity of hardware choices. Switches appear in configurations as small as four ports, such as the one offered by McData in its Sphereon 4300, while directors are available in port counts as high as 256 from vendors such as Inrange, Sandial and Sanera Systems (see "High-end storage switches").

These FC switches and directors offer benefits that uniquely qualify them over other networking protocols for moving block I/O between servers and external storage arrays. In addition to FC's ability to efficiently move large block I/O, these switches have expanded their legacy transport services such as data integrity, routing and trunking to offer enhanced functionality such as 4Gb and 10Gb FC, virtual and partitioned SANs, improved security and better vendor interoperability.

One nuance of the FC protocol that helps to ensure data integrity and sets it apart from other networking protocols is the requirement for all data frames to arrive in sequence. Unlike TCP/IP, which can reassemble data packets of information regardless of the order in which they arrive at their destination, the FC protocol requires that data frames arrive in the same order in which they were sent. This creates difficulties for performing advanced functions between different switches, specifically routing and trunking between switches from the same and different vendors.

How the routing and trunking functions get handled by the different switch vendors continues to be a bone of contention between them. While all vendors support the current FC standard of connectivity between switches using ISLs that assign ISLs to servers based upon a round-robin distribution methodology, Brocade's switches users treat up to four separate ISLs as one logical path.

This feature offers significant advantages over the current FC standard. First, this capability treats four physical ISLs as one logical ISL. Second, it allows for the gathering of meaningful historical performance information because under the current FC standard, there's no reliable way of knowing which ISL any particular server is using. Under the current standard, every time a server logs off and back onto a FC fabric, the server may be reassigned a different ISL using the existing round-robin methodology when multiple ISLs are in place.

Finally, Brocade's trunking reduces the number of ISLs needed between switches. The trunking function can aggregate the bandwidth and utilization of their links, treating four 2Gb ISLs as one logical 8Gb pipe. Under the current FC standard, four separate ISLs are exactly that, four 2Gb pipes with a maximum capacity of 2Gb each that lacks a nondestructive mechanism to allow an overloaded ISL to send some of its FC traffic down another lesser-used ISL.

The dispute between existing vendors arises not in the value of this technology, but in its implementation. Brocade deploys this technology using its proprietary hardware ASIC solution. While users have the option to turn this feature off on Brocade gear and connect ISLs to another vendor's switch, the feature is currently an all-or-nothing option on Brocade switches. So unless users exclusively use Brocade switches and directors, they lose this important value add.

A larger issue grating on users emerges in terms of how vendors choose to deploy ISLs. For those users who need to link switches together, the only way to do so now is by consuming some of their existing ports for ISLs, as opposed to having these switches offering back-end ports that provide for this functionality. While annoying, users bristle when vendors tell them there is no demand for this service. At the fall Storage Decisions 2003 conference, Sanjay Mandloi, a vice president with LabMorgan Technology Solutions of JP Morgan Chase, stated that both JP Morgan and Merrill Lynch are asking vendors to provide this functionality.

This was first published in November 2003

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