How far can the fcal cable be and what sort of performace hit do you take on that 3rd loop (since each loop can only consist of 8 shelves)?
As far as performance goes, the three FCAL loops are peers in the system. They are "parallel". Each loop is independently connected into the system via its own FCAL adapter/controller and there is no significant prioritization of requests/responses on any one loop over another.
You figure, the last shelf in the 3rd loop is going to be more than a few meters away from the filer...
Well yes, but distance-from-the-controller is not a significant influencer of device performance on an FCAL loop. This type of fibre channel incorporates some cunning stunts at the MAC layer, borrowed from Token Ring and FDDI, that do an effective job of spreading the available bandwidth betwixt all of the connected players, regardless of their physical position on the loop.
Keith
+--- In a previous state of mind, "Keith Brown" keith@netapp.com wrote: | | As far as performance goes, the three FCAL loops are peers in the system. | They are "parallel". Each loop is independently connected into the system | via its own FCAL adapter/controller and there is no significant | prioritization of requests/responses on any one loop over another.
Is this true in a clustered failover environment as well or can I tag the failover loops as having a lower priority than the "local" loops? I know, this can lead to starvation (elevator theory) if mis-handled but it could also allow the user to fine-tune their CF setup to their needs.
| Well yes, but distance-from-the-controller is not a significant influencer | of device performance on an FCAL loop. This type of fibre channel
There must be some guidelines though. I would think that you would not want to keep all the loops within some reasonable distance. That is, I would probably want to put my filer in the middle of the rack so all loops are semi-equal as opposed to at the end of the rack (thinking that a filer that takes up 3 racks with 3 fully populated loops).
I am sure the degradation, if any, is not noticeable. Otherwise NetApp would probably stress very precise setups :)
| incorporates some cunning stunts at the MAC layer, borrowed from Token Ring | and FDDI, that do an effective job of spreading the available bandwidth | betwixt all of the connected players, regardless of their physical position | on the loop.
Indeed. fcal is quite spiffy. I still cannot get over the connector being 2 wire pairs in a db-9 connector. I suppose a $5 cable from the local computer store would not really work well in a pinch, eh?
Actually, why the decision to use copper instead of fiber?
Thanks.
Alexei
| | Keith |
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Keith Brown