HBA Transfer Rate Calculatons..

[Stuart Abramson_2]

Here are some Fiber Channel transfer rate ratings:

..EMC FA:........................2 Gbit/sec
..EMC Connectrix Switch Port:....2 Gbit/sec

..HP-UX FC HBA:................200 MBytes/sec

Of course they rate them in different units. Since I only care about Bytes, I have to convert 2 Gb/s to MB/s, where:
..B - Byte
..b - bit

gives me:

..2 Gb/s * 1000 Mb/Gb
..------------------------ = 250 Mbytes/sec
.........8b/B

So, the FA is 250 MBytes/sec and the HBA is 200 MBytes/sec.

So, how can I have a "Fan-In" ratio of UNIX server HBAs to FAs of 6 to 1?

Are there "utilization" stats like an HBA is only 75% efficient and they only run 60% of the time?

do you divide by 8 to convert bits to bytes? Or do you divide by some other number (start/stop bits?)?

Is there some explanation for figureing this somewhere?

[harry d brown jr]

Fibre Channel I believe is 12 bits to the byte and of course the slowest link is going to be your disk drives.

As far as FAN-in/out, refer to EMC's supported matrix.

live free or die
harry

[Alzhy]

2Gbps Fibre is essentially ~ 200 Megabytes/sec or ~400 Mbytes/sec both ways.

If you suspect the Fibre between your EMC and the Connectrix is loaded, you can log in to the switch or the web front end and display port statistics.

As far as fan-in ratios, YMMV IMHO.. it depends on your envirnment and how heavily loaded (and heavy processing windows)your servers are.

[Stuart Abramson_2]

Harry: How can I find out if FC is 12 bits/byte or 8 bits/byte?

Nelson: Are you saying that the FC transmists and receives concurrently? Probably not to the same disk at the same time, but to two different disks on two different disk directors? (All writes are to cache - I guess all reads are from cache also.)?

[Jeff Schussele]

Hi Stuart,

Yes - FC has separate receive & transmit lines & *can* communicate in full duplex.
SCSI HBAs have 8 separate lines for each bit in the byte, but they are half-duplex lines therefore they can only transmit OR receive at one time.

Rgds,
Jeff

[Alzhy]

Yes.

FC transmits/receives concurrently -- full duplex operations.

For most arrays on a SAN Fabric, the SAN switch to the array's front (or host ports) can become overwhelmed -- if say, on the front end or host port several servers have LUNs presented to it. Imagine say 4 servers each with 2 HBA's .. and each HBA has a LUN each.. so a total of 8 LUNs on 8 FC-HBAs feeding that lone (or pair) of Array port can sometimes overwhelm the bandwidth .. specially of the array is cache-centric..

I always plan out my enterprise storage layouts to avoid such 'possibilities'..

[curt larson_1]

actually, the fc-1 transmission protocal uses a encoding scheme that encodes 8-bit bytes into 10-bit transmission characters.

so transmitting 2Gbits/s is only delivering 200Mbytes of data.

then on top of that you have the overhead of the fc-1 ordered sets and the fc-2 framing protocol

[Hein van den Heuvel · Accepted solution]

Uwe Zessin has provided a couple useful replies in this space in the past.
Basically FC uses 10 bits to transfer 8 bites using a 8b/10b table. This is done to avoid long series of zero's or ones.

So.. just divide by 10 to go from bits to bytes.

See:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=583396

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=549070

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=467013

hth,
Hein.