topic Re: fabric versus arbitrated loop in HPE EVA Storage

fabric versus arbitrated loop

HPADM — Fri, 13 Sep 2002 12:35:38 GMT

Hi!
I would like to get some information about fabric and arbitrated loop topology.
When do I have to choose one instead of the other one?
Could you give me some example?
Thank you.

Re: fabric versus arbitrated loop

Sanjay_6 — Fri, 13 Sep 2002 12:46:29 GMT

Hi,

Try this link from ITRC cookbook,

http://us-support.external.hp.com/iv/data/documents/DE_SW_UX_swrec_EN_01_E/FibreChannel.pdf

Hope this helps.

Regds

Re: fabric versus arbitrated loop

Leif Halvarsson_2 — Fri, 13 Sep 2002 12:59:49 GMT

Hi

Very short:
loop: HUB (loop) network,limited number of devices, workgroup and department solutions.
fabric: switched network, very large number of devices, enterprise solutions.

Perhaps this link can give you a little help.

http://www.networkcomputing.com/1109/1109ws1.html

There is plenty of information about this on Internet.

Re: fabric versus arbitrated loop

Vincent Fleming — Fri, 13 Sep 2002 13:43:22 GMT

One thing to note about fabric vs loop...

You can direct-attach from a host to a disk array or tape device via loop, but you cannot with fabric mode.

As a general rule, I like to use loop only in direct-attach situations; if I've got a switch in the config, it's in Fabric mode.

There are exceptions, however. When working with older equipment ("older" here meaning about 2-3 years or older), often the older devices do not support Fabric mode, and you are therefore forced to use loop mode. There are modes you can set in the switches to help in mixed-mode configurations. Mixed-mode configs are something to be avoided, if possible.

Good luck!

Re: fabric versus arbitrated loop

Michael Tully — Sat, 14 Sep 2002 06:55:37 GMT

When using fabric, constant traffic will be able to stream from many devices and hosts, whereas using loop, only one device in the loop can actually transmit data. Others wishing to transmit data wait their turn. Direct connecting is okay using loop, but in a switch definitely use fabric.

Re: fabric versus arbitrated loop

Quin Hammes — Mon, 07 Oct 2002 17:13:59 GMT

Everyone is right but the biggest difference is that a 100 MB/sec loop hub can only do 100 MB/sec for all traffic on that hub.

A 16 port switch should be able to do 100MB/sec per port (16 *100=total throughput).

This is a very important difference.

If you are using multiple computers which need to communicate at the same time to devices on the loop/fabric then go with fabric.

If you need more throughput than 100MB/sec total then go fabric.

Loops are good in active/passive cluster environments. Loop is much cheaper also.

Quin

Re: fabric versus arbitrated loop

Insu Kim — Wed, 09 Oct 2002 03:48:15 GMT

From performance perspective,
Arbitrated loop is like Token Ring which means bandwidth is shared across all the devices in a loop whileas Fabric is switched network so that it guarantees non-blocking throughput across all the ports in the switch.

Re: fabric versus arbitrated loop

Insu Kim — Sun, 13 Oct 2002 14:23:46 GMT

I quoted the statement below in the book titled "Building SANs with Brocade Fabric switches".

Hubs can be used on small SANs to interconnect devices in an arbitrated loop topology or connect two devices directly. Hubs should not be used when there is more than one active host, since there will be more competion for the limited bandwidth of the loop. The more hosts that are added to the loop, the less efficient it is, because a larger percentage of time is spent arbitrating for control of the loop than actually transmitting data.
Remember that a switch creates circuits to maximize bandwidth, while all devices plugged into a hub share the bandwitdh of one line.

Hope this helps,