More SCSI vs. Fibre Channel

Posted on January 01, 1999

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More SCSI vs. Fibre Channel

Eric Case

Cross Platform Digital Imaging Group Inc.

I read with mounting consternation the Opinion article on page 62 in the November issue of INFOSTOR ("SCSI vs. Fibre Channel Drives"). My response follows.

All the benefits of Fibre Channel at the drive level were ignored completely. Mr. McGarrah states that Fibre Channel drives "cannot meet two critical requirements for enterprise-class storage: easy data management and backward compatibility."

Ease of data management: As one of the many manufacturers of Fibre Channel and parallel SCSI subsystems, we supply enterprise-class management tools for both Fibre Channel and SCSI storage solutions. The Fibre Channel tools if anything make managing large storage environments much simpler. Additionally, Fibre Channel tools allow easy configuration of enterprise-class facilities such as remote mirroring and dual loops for redundancy. This is very difficult, if not impossible, with parallel SCSI.

Backward compatibility: This is an old chestnut that every manufacturer brings up when they don`t have the latest technology shipping and wish to muddy the waters of progress. There is absolutely no problem in continuing to use older SCSI drives in a system and also introduce new Fibre Channel technology. In contrast, who in their right mind would mix 50-pin narrow SCSI with 68-pin wide SCSI on the same bus if they want the higher performance? No one. Who will put wide SCSI on the same bus as Ultra2 SCSI if they want the higher performance? Again, no one. This does not mean that you have to throw out the older drives; you just deploy them on the less performance-critical data. This will be exactly the same in future generations of Fibre Channel. With Fibre Channel switch technology, this segregation--if ever required--is a very simple matter of placing subsystems with different characteristics on different ports. This avoids the situation Mr. McGarrah highlights as an Ultra160/m benefit--that is, having to step down data transfer rates when Ultra SCSI drives are intermixed with Ultra160/m drives.

There are currently no parallel SCSI switches available. Fibre Channel is available now. Full-scale implementation of Ultra160/m SCSI is most likely going to be available in 2000-2001. By then, Fibre Channel will be at 4GBps.

Using Fibre Channel drives in RAID systems makes great sense. People buy RAID for fault tolerance. Unlike SCSI drives, Fibre Channel drives have dual ports, allowing full redundancy to the drives. Additionally, Fibre Channel drives provide much higher reliability because dramatically fewer pin interconnections are used than in a comparable SCSI system and, of course, Fibre Channel can scale much more than SCSI--up to 126 drives per controller.

Last, but not least, with all the added benefits that Fibre Channel drives bring, they cost the same as Ultra2 LVD SCSI drives!

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