Page 11 of 12 July 2001 Why Choose Native Fibre Channel Backup? What if you aren’t ready for a SAN? If you’re not quite ready to implement a SAN, should you stick with SCSI or move to Fibre Channel when you need to add more backup resources? While SCSI is a well-established, reliable standard for backup devices, you may find that SCSI backup is no longer sufficient for your expanding network.  SCSI limitations on distance between devices, number of devices supported, and bandwidth shareability may make Fibre Channel a better choice for your backup systems. Distance between devices SCSI is capable of high data transfer rates (up to 80 MB/second for Ultra2 SCSI and 160 MB/second for Ultra3), but these rates can only be achieved over short distances (up to 12 meters for multiple devices).   Fibre Channel can support distances of up to 10 kilometers between devices while still providing high data transfer rates (100 MB/second now, 200 and 400 MB/second in the near future).  The distance capabilities of Fibre Channel not only facilitate remote backup, but open up options for the placement of backup devices within a business facility. Number of devices The maximum number of devices that can be connected to a wide SCSI bus is 16.  This inhibits sharing of tape libraries between servers because a large library and its drives may use up most of the available SCSI IDs.   The basic Fibre Channel configuration, an arbitrated loop, can support up to 126 devices, and switched fabrics can support millions of devices.   Even without a SAN, you can easily share a Fibre Channel tape library among multiple servers and their disk systems. Bandwidth shareability All of the devices on a SCSI bus must share the bandwidth of the bus.   This means that all of the tape drives in a library may be competing for bus access at the same time.  When multiple devices are attached to a SCSI bus, complex arbitration and addressing protocols are required to control bus access and manage data flow.  The processor overhead required to manage the bus degrades the performance of all the devices on the bus. In contrast, Fibre Channel provides greater bandwidth with simpler arbitration and addressing protocols.  In a Fibre Channel arbitrated loop, tape drives take turns as on a SCSI bus, but access to the bandwidth is more efficient.  In a switched fabric, all of the tape drives in a library can use the full bandwidth of Fibre Channel simultaneously. Even if you don’t have a SAN, SCSI limitations may make Fibre Channel a better choice for your backup systems. p1   p2   p3   p4   p5   p6   p7   p8   p9   p10   p11   p12