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You should be familiar with the following
The top line of Figure 4-1 shows the workstations. They are connected to the LAN, as expected. The client view of stored data will not change in a SAN. The only expectation is that there should be some relief from storage bottlenecks, and data should be available when a SAN is used.
Windows NT and IBM mainframes could just as easily appear in the illustration, although it would be reckless to say that interoperability concerns have been worked out. At the very least, heterogeneous servers can be connected to the SAN, and we are moving toward the day when each operating system better recognizes the file systems of the other operating systems.
Note that the servers have a single card in them, called a Fibre Channel Host Bus Adapter. In the balance of this chapter, you ll usually see two HBAs in each server, as multiple HBAs are an important part of fault-proofing a SAN.
The next row is the SAN, made up of various combinations of hubs, switches, and FC-SCSI bridges. The SAN is frequently represented as an ellipse (or a cloud, in the case of fabric-switched SANs). Whatever graphic is used, the idea is to broadly suggest an any-to-any connectivity of devices on the SAN. In fact, a Fibre Channel Arbitrated Loop (FC-AL) is really a loop. A switch is an any-to-any star topology. A bridge is a device that has both Fibre Channel and SCSI connections, allowing SCSI devices to be attached to the Fibre Channel network.
The SAN, of course, is the connection infrastructure between servers and storage devices. The connection medium is usually fiber
At the bottom are the storage devices. The typical primary storage device on a SAN is the high-availability disk array. However, the JBOD (just a bunch of disks) is still with us. The JBOD is commonly a collection of SCSI disks in an enclosure, but Fibre Channel JBODs are available, too. The JBOD disk farm or disk hotel is still useful for meeting some data center needs.
The typical secondary storage device is the tape library. Although single-mechanism tape
Magneto Optical devices
SAN components form something like a high-tech Lego set, so in order to build a SAN, we should be familiar with what each piece can do.
As stated in the preface, we use HP equipment in our examples. This is not an infomercial for HP, which we leave to HP s product briefs and Web site. It is simply because we are most familiar with this equipment and have worked on the
Fiber optic cable capabilities.
That s not a spelling error.
optic cable. The fiber optic cable may be 9 micron single mode, and can be used for distances of up to 10 km. The cable may be 50 micron multimode (distances to 500 meters) or 62.5 micron
HP s two Fibre Channel hub offerings are good models for hubs in general. The shortwave hub (called the HP SureStore E Hub S10) has ten ports. It can be cascaded into one other
The longwave hub (the HP SureStore E Hub L10) has 10 ports. It can be cascaded into one other longwave or shortwave hub. The longwave hub is the right one for distance requirements of up to 10 km, using 9 micron cable.
Bridge capabilities. The HP FC4/2 Bridge has two Fibre Channel ports for connection to the SAN. It has four SCSI ports for connection to SCSI devices.
Hewlett-Packard configurations use the Brocade 2800 switch. It is a 16-port fabric switch with the capability of cascading or meshing switches into very large
Disk array capabilities.
A typical disk array is Fibre Channel-enabled, and provides substantial storage capacity. The high-availability features of a disk array are hot-swappable fans, power
JBOD capabilities. JBODs are still with us, in both SCSI and Fibre Channel versions. The HP FC 10 as a Fibre Channel JBOD. The HP SureStore E Disk System SC10, a SCSI JBOD, is a good candidate for a SAN. It has ten 9 GB or 18 GB drives for a maximum capacity of 180 GB per enclosure. Also, each device takes up only 3.5 EIA rack units, so you can rackmount up to ten of them in a rack, yielding 1.8 TB. The high-availability features of a modern JBOD are hot-swappable fans, power supplies, bus control cards, and disk drives.
There are a number of terms
Since RAID technology reduced the impact of lost data in terms of a disk failure, it was only natural that disk array designers turned to other
The point of redundant components is, of course, to allow the device to keep working until the defective part can be
There are event monitoring and alerting capabilities in almost every component on a SAN, to alert you to component failures. One useful advancement in high-end devices is the phone home capability, found in the HP SureStore E Disk Array XP256. When the disk array senses a failure, it contacts HP service so immediate action can be taken.
Even HBAs report failures as events, and their onboard LEDs are also a good indicator that something is wrong. The more recent HBAs have customer-
Hubs shut down failed ports, and as hub management software
Multiple paths to a device is an important concept in a SAN. And it s easier to ensure multiple pathing in a SAN than it is in a arrangement of SCSI mass storage devices.
Even defective fiber optic cable can be
Assumptions about power. Take care of your power. Even the best planned SAN is susceptible to power outages. The uninterruptible power supply (UPS) or standby generator can be your best friend. It also helps to have a reliable power company.
If an earthquake or
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