topic FC HDD vs SCSI HDD in Disk

FC HDD vs SCSI HDD

Oleg Mochkin — Wed, 31 Mar 2004 02:03:01 GMT

What is main advantage FC disks over SCSI ?
Oleg.

Re: FC HDD vs SCSI HDD

Karthik S S — Wed, 31 Mar 2004 02:43:32 GMT

With FC harddisks you get better througput. Also the number of devices than can be connected to a FC Loop (128 devices) /fabric (in millions) is far more compared to SCSI (max 15 devices).

Also refer,
http://www.storagereview.com/guide2000/ref/hdd/if/sfFCAL.html

-Karthik S S

Re: FC HDD vs SCSI HDD

Wayne Rippy — Thu, 08 Apr 2004 15:37:14 GMT

Agree, typically you find faster read/writes, and you are able to have more disks in a set.

However, I would caution that if you are looking to purchase a new "SAN" that you look at the overall environment. Just because the disks are capable, and are able doesn't mean they will read or write faster. Alot of that depends on through put from the application on the server, through the HBA's, to the controller cache. Then the 'ack' given back to the 'requestor' or server sending the data, and finally a destage of cach to disk.

The performance of FC disks is most notable with small block data in non-sequential writes (i.e. causing cache to destage to disk constantly).

Keeping consistant with the forum, I will refrain from speaking of 'other architecture' from other vendors. In general the architecture of HP/Compaq SANS is the same. So this 'scenerio' of writing small block data over and over non-sequentially is really the only place a performance increase might be seen.

Re: FC HDD vs SCSI HDD

Hein van den Heuvel — Thu, 08 Apr 2004 19:17:36 GMT

The FC speeds can be a lot higher
(1Gbit/2Gbit) over longer distances with no electrical interference.

The high speed wide copper scsi only accepts relatively short distances, the cables are short, heavy and thick. You can get electtricl connection problems (ground loops) and can receive (and send) electrical interference.

fwiw,
Hein.

Re: FC HDD vs SCSI HDD

Uwe Zessin — Fri, 09 Apr 2004 03:11:02 GMT

Today's FC disks have dual-port active/active connections. That is nothing new - I already have seen dual-ported disks in the eighties and I won't be surprised if such disks have existed for a much much longer time.

Of course, that is highly needed. If one device blocks a parallel SCSI bus (15 devices) or one FC-loop (on the EVA up to 56 devices [1]) - the game IS OVER on that communications channel!

[1] Any EVA with more then 56 disks (=4 disk drive enclosures) should have been equipped with loop switches that provide better fault isolation. In case such a switch fails, you still have a second switch on the other loop.