SCSI AND FIBRE SPEED

[SAM_24]

Hi,

I want to know what is speed of data flow between server and storage array using scsi and fibre channel adapters.

Is this right?

SCSI3 - 40M MByts/sec
Fibre - 100 MBytes/sec.

Thanks.

[Wodisch_1]

Hi,

this is solely from memory:
Ultra Fast Wide Differential SCSI3 = 160MBit/s
FC1 = 100MBit/s (but you get only about 90)
FC2 = 200MBit/s (no experience here)

FWIW,
Wodisch

[Paula J Frazer-Campbell]

Raj

Remember that the speeds quoted are only in optimum contitions.

It is the "It depends" answer on what speed you can actually get in a real environment of reading and writing files.

Some factore are:-

1. The speed of the media at the other end.

2. File sizes.

3. Dir structures.

4. Structure of your data (Mirror / Stripe ?)


Paula

[Stefan Farrelly]

It depends on what you call SCSI3 - this is normally defined below as either Ultra SCSI or Ultra2 SCSI etc.

SCSI bus speeds:

Slow-Narrow: 5 MB/s
Fast-Narrow: 10 MB/s
Slow-Wide: 10 MB/s
Fast-Wide: 20 MB/s
Ultra-Narrow: 20 MB/s
Ultra-Wide: 40 MB/s
Ultra2-Narrow: 40 MB/s
Ultra2-Wide: 80 MB/s

Fibre is supposed to be 100 MB/s but I have never seen it - the bus on the HP's doesnt seem to be able to go any faster than 60 MB's - thats the fastest ive seen on N's and L's with a single channel fibre being tested (and if its cached on the disk array, if not cached at the time only arund 50 MB/s).
Again - the above speed for Ultra2 Wide at 80 MB/s is design speed - an HP server would be very unlikely to keep up, again I suggest the max is about 60 MB/s (a single disk couldnt do this you would need something like a disk array on the other end with lots of cache).

[Michael Lampi]

Stefan's answer is the most accurate. However, he forgot the fact that there is no narrow flavor of Ultra-2, and left off Ultra-160 SCSI completely.

Ultra-160 SCSI has a data transfer rate of 160 megabytes per second during the data phase. When combined with the command setup and other delays, the resulting speed is of course somewhat less.

In the near future the Ultra-320 SCSI will be fairly widely available. This is somewhat humorous in that most computer buses these days would be hard pressed to handle long term transfers at that speed.

Lastly, the newer fibrechannel controllers can transfer data at 200 megabytes per second. Again, due to command overhead and processing, though not quite as severe as SCSI, will reduce the overall throughput from this value.

[harry d brown jr]

Michael,

Ultra-160 is 160 MegaBITS, NOT BYTES. In megabytes, it would be 16 megabytes a second. Of course all the ratings are in perfect LAB conditions that usually can't be reproduced within the same LAB twice anyways, so it's always a good idea to assume that you are only ever going to get 50% of the rated speed.

live free or die
harry

[Erik Tong]

First, here's a link to some intereting information on SCSI:
http://scsifaq.org:9080/scsi_faq/scsifaq.html

Judging from this information, Ultra160 has a BUS speed of 160 megabytes. A bus speed of 160 megabits (20MB) could hardly be called "ultra".

As others have noted, most computer (PCI) buses can't keep up with that bus speed. Actually, disk drives can't keep up either (15-30 megabytes/s peak). Why have that fast a bus? Multiple disks on the bus, or a disk array can pump out more MB/s. On the other end, computer bus speeds will catch up, or multiple computers can be attached to the bus.

If you're just attaching one server directly to the storage, parallel SCSI (Ultra SCSI) is the way to go. Some hosts, like HPUX, even support 2(?) initiator parallel SCSI bus connections (make sure the disk supports it to). Simpler to use and just as fast.

If you plan to network your storage Fibre channel may be the way to go instead. It's expensive and not always the easest to use. It can, however solve difficult storage sharing problems like off site backup (parallel SCSI is very limited in distance between the server and the storage, FC devices can be 5 km+ appart).

Regards,
Erik

PS - technical egg head note: SCSI3 is a standard that includes Fibre Channel. It's physical transport specifications that really define the between Ultra SCSI (LVD,FastSCSI,etc) and fibre channel. Ultra SCSI uses a parallel physical interface and fibre channel uses a serial.

[Vincent Farrugia]

Hello,

SCSI3 is 160MBytes/sec, not 160MBits/sec fast. That is the speed for the Wide 16-bit SCSI, which is the only standard available for SCSI3.

Fibre Channel is 100MBytes/sec.

For more information, go to:

http://scsifaq.paralan.com/scsifaqanswers.html#17

and

http://scsifaq.paralan.com/scsifaqanswers.html#20

HTH,
Vince