Adding a third 3800 switch to existing fibric.

[Zapdoper]

We currently have a SAN that is used only for backup infrastructure. Mostly for NDMP backups of Netapp filers. Currently our SAN is made of two silkworm 3800 switches. We need to extend the SAN connectivity to another floor in the same building and are considering a third 3800 switch since we don't need that many ports. The first two switches are connected with 2 ISLs on port 0 and port1 of each switch. I'm trying to find out what's the best way to connect the third switch? Using two ports 0 and 1 and have two ISLs to second switch? Using 4 ports have two ISLs to second switch and two to the first switch?

Any thoughts are appreciated.

 

[jjjon]

Zapdoper, if you have the ports, I would certainly connect the new switch to both of the existing switches. If you have a node on the new switch that needs to communicate with a node you have on the unconnected switch, it will have an extra hop between your 2 existing switch, that depending on your config, might reduce performance.

Also, I wouldn't put ISLs on port 0 & 1. I believe the ports in the 3800 are in quads, so in theory you could lose ports 0-3 together, so have one on port 0 and the other on port 4.

 

[Breslau]

the concept of quads on a 3800 really only comes into play when you're talking about trunking. i believe this switch uses a single ASIC, so to me the poster can put the ISL's where ever on the switch. conceptually, they may want to place them on the same ports on each switch for the sake of consistency.

now, if they're trunking, then both ends of the ISL need to match up in terms of port numbers.

otherwise, as you said, i'd hook all three switches together. this would give you a circular topology and buy you a little bit of resiliency, ie a single switch outage won't necessarily mean your entire fabric is down.

the other thing that needs to be considered is the distance between this new switch and the other two.

 

[comtec17]

The 3800 has 4 ASIC's or 1 per Quad. As BeasterBob states, unless you are trunking, spread your ISL's across 2 Quads for redundancy.

Comtec17
BCFP since 1998

 

[Breslau]

Actually, we're both wrong. the 3800 has two Bloom ASICs.

sorry, it's been a while since i've read the specs on this switch. i just knew it didn't have 4....

anyway, so if you want to accomplish what's described above, then you could put a line into the first 8 ports and another in the upper 8.