Sam: The back end refers to the interface used at the disk level, the
front end is what the host subsystem has. Up until the time FC entered the market, most RAID vendors used a fast-wide-differential
host interface, but had fast wide single-ended drives.
This was purely for cost, as single-ended drives cost less, and the reason for differential signals is that they provided distance, and cleaner data when approaching the SCSI transfer limits.
The reason for FC at the host should now be obvious, however at the back end, there is no benefit for several reasons, in no particular order.
1. Cost. The electronics on FC drives cost almost double than the electronics on parallel SCSI drives. (The mechanical parts are all the same, and most vendors standardize on a design, then just change the interface electronics.
2. Sourcing - Only seagate is shipping a FC drive, since there are allocation problems with newer technology, then vendors can't risk a supply problem preventing product shipments. When IBM and Fuji ship production product, this will get better.
3. Cost - You have to add more expensive silicon to interface with a FC drive, because the frequency is higher; when a FC drive fails, all the drives on the path will become unavailable without additional work; there are many more SCSI chipsets for engineers to choose from, that are extremely fast, and rock solid. The same is NOT true for FC.
Finally, FC drives just don't outperform SCSI drives! We are limited to the physics of the mechanical "stuff". Look at the seagate pages and study them. You will see that although the interface is faster, the drives don't access data or transfer information any faster. As a designer, you always want to adhere to the KISS principle, "keep it simple, stupid".
--->
Veritas: They are much better off in SANs, because they deal with the filesystem, which is the key. The VxFS (veritas file system) is bundled with HP, SUN, IBM and other vendor's UNIXs. Since the purpose of a SAN is shared DATA, not shared access, then they are well positioned. As you might also know the newest version of NT also implements a version of the veritas file system.
David
|
