Case then said, "When those silkworms are in their cocoon's you can't tell what they're doing". Staying tuned in MI. The SAN seems to really be picking up the rate of change now.....
Down on the Data Farm: Reap the Rewards of FC-AL
David Harvey
Don't look for amber fields of grain on the hottest farms of the 21st century.
And don't expect John Deere to keep those farms in order; that's a job for
FC-AL (Fibre Channel-Arbitrated Loop) and SANs (Storage Area
Networks). These tools will form the infrastructure of sprawling data farms
containing tera- and petabytes of data. Individual nodes up to six miles apart
will link campuses and WANs until a pulsing net of data covers the world.
The data flowing through those pipes can be roughly divided into three types:
- Transactional: Hundreds of small files processed at once.
- Data warehousing and large files: Big chunks of data are passed around
frequently.
- Very large file or data streaming/video: Huge files stream to users in real
time.
FC-AL's advantage today lies in the third category. SCSI still has the edge in
speed and cost for transactional data processing, thanks to multichannel SCSI
devices. Sporting as many as six channels of SCSI, each independently
accessible, multichannel SCSI installation can send many more small
transactions at once than a single-channel FC-AL device. And multichannel
SCSI systems' production costs have decreased over time.
While FC-AL is-per channel-faster than SCSI, there are no multichannel
FC-AL devices in production. The key is multichannel FC-AL adapters' price
point; it must be sufficiently attractive to lure buyers from established,
cost-effective technology that performs well enough to a relatively unproven
and expensive technology that sends performance through the roof.
To get a handle on the new and relatively small FC-AL market, we surveyed
manufacturers of Fibre Channel storage and networking hardware. The
responses indicate that storage hardware is gaining the most ground;
FC-AL-based RAID devices in particular are pushing into the various
channels.
Fiber Serial This fiber may not be your mother's All-Bran, but it will keep your
system running smoothly. FC-AL's serial architecture sends whole packets
through the pipe, enabling very large files or streaming data/video to move to
specific network nodes. Parallel architectures, such as standard SCSI, are
slower because they break down each packet into a set number of elements,
which travel through the wire to the receiving device where the packet is
reassembled. But the main reason for FC-AL's speed is that it's pure gigabit
technology.
As with any external peripheral, FC-AL's speed is limited by the adapter card
and host bus. We were surprised to see that few vendors are working with
I2O technology (see our Interactive Buyer's Guide at
www.networkcomputing.com/1002/1002buyers.html); Intel's I2O-compliant
Pentium II and Xeon processors offer off-loading interrupts and slot-one
RAID to maximize FC-AL's speed. Time has shown that cache alone will not
provide the boost needed to align adapter speeds with the speed of the data
subsystem. On the plus side, FC-AL devices deliver hot-swap networks able
to switch out individual drives and entire devices.
If you're considering FC-AL devices, you're probably dealing with huge
streaming files, so consider both capacity and ability to upgrade very carefully.
And if you need high levels of administrative support, you'll find plenty of it
built into these products-almost all have out-of-band management features.
ANDATACO's GigaRAID/FC provides direct terminal connections via the
serial port. Devices higher up the ladder, such as Raidtec Corp.'s FibreRAID
PCI/Fibre Array let you dial directly into the array. HTTP-based management
is on the rise, and support for multiple administrative standards is also
excellent. For example, nStor Corp. supports SNMP, Compaq Computer
Corp.'s Insight Manager, Hewlett-Packard Co.'s OpenView and Novell's
ManageWise; Synaptic Systems Corp. delivers support for SNMP, DMI
(Desktop Managment Interface), Insight Manager, OpenView and Microsoft
Corp.'s Management Console.
If distance concerns have brought you to FC-AL, you're in luck. Vendors
recently have mastered the art of long-distance fiber. The distance winner is
Jaycor Networks, with its 3-kilometer (km) connection, followed by
ANDATACO's 1.5-km hookup, and 1,500-foot setups from CLARiiON
and Raidtec.
The LAN in SAN FC-AL extends beyond the host to peripheral connections
allowing for the creation of FC-AL-based storage networks, commonly called
SANs. Toss a few workstations, some servers and the storage peripherals
together over existing network technology and you have a standard LAN. But
link those same components via FC-AL and you have a SAN. Connection
points to the Ethernet network are supplied by those servers and workstations
with both FC-AL and Ethernet adapter cards.
Be especially careful when you first bring a SAN in-house. Record "before"
and "after" performance and traffic data, and keep the two networks as far
apart as possible. Limiting points of contact will make it easier to record
statistics while reducing the risk of errors. Keeping duplicate data sources is
essential when building, installing and testing your SAN; mirror between LAN
and SAN data sources for several months after your SAN goes online. This is
not paranoia-by adding a new network that is accessed from an existing
network, you create a high level of complexity, and heightened risk. You
should also limit user access to the SAN while mirroring SAN data to the
LAN. If the SAN goes down, users need only remap their client systems back
to the LAN.
Bear in mind that this absolute data safety lasts only as long as you have a
redundant LAN and SAN. This condition is intended only for testing and will
cease when you put your SAN into production. At that point you'll need to
make use of either FC-AL- or SCSI-based backup storage devices and
appropriate software to safeguard your data.
The lowliest component in any network is the NIC. It's also the most critical in
terms of overall performance. Emulex Corp.'s LP7000/E Host Bus Adapter
comes with a standard GLM (gigabit-linking module) for copper or fiber
hookups; it includes support for Microsoft Windows NT, SunSoft Solaris
2.51 and IBM AIX 4.1 for both SCSI and IP protocols, and Novell
NetWare, UnixWare 2.1 and Apple Computer Mac 7.5.3 or greater for
SCSI. Kudos to Emulex for stating the real-world performance of its adapter:
The company promises to deliver "over 85 MB per second." Look to Emulex
as well for the incredibly low-priced LP3000 adapter. At $595, this
bare-bones, copper-only card supports NT alone, but will work with many
FC-AL peripherals.
Next up the food chain comes the hub. In FC-AL's loop-based architecture,
the hub creates a star topology-each node has a separate, distinct path to the
hub. This not only increases overall reliability, but ensures that the loop will
continue functioning if a node is beset by a critical malfunction. Starting with
the hub is probably your best bet when building a SAN. For fledgling
networks, hubs provide enough power and let you take stock of your
network, letting you plan where you'll put high-end devices such as switches
and switching hubs.
FC-AL on a Budget Emulex's LH5000 Digital Fibre Hub delivers all the
features of an FC-AL-based SAN for between $2,500 and $3,000; these
hubs support eight copper or fiber ports and include a 10BASE-T Ethernet
management port. The hubs' best feature is their ability to force ports into
bypass mode, instantly isolating the loop from any problems.
Switches, switching hubs, routers and the like form the highest level of any
network infrastructure. McData Corp.'s high-end products can cost hundreds
of thousands of dollars. Prices for its bleeding-edge switch, the ED-5000
director, start at $120,000. It delivers 32 full-duplex ports, letting you
"hot-link" servers and storage devices. It sports redundant fans, power
supplies, controllers, processors and memory modules. Similar in function and
price is Computer Network Technology's UltraNet Storage Director. Both
companies also offer switches in the $50,000 range.
It won't be long before there's a wide demand for FC-AL. We strongly
suggest you begin acquiring the technology now. If you can set up even a small
test FC-AL network, it will pay off a thousandfold when you ultimately switch
over one or more departments.
And don't scrap SCSI. It will not suffer the same fate as MFM and RLL
drives. While IDE, EIDE and ATA may all fall by the wayside, SCSI has a
strong future on the low end, in transactional markets and in end-user systems.
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