SAN speed negotiation.

[white221g]

Folks,
Please help me out with this:
1) What decides the speed of the SAN?. The switch speed, Array port speed or HBA speed?.

2)At what speed will the Storage array port, switch port and HBA operate if:

a) Storage array port is 4gbps, switch is 4gbps, but HBA is 2 gbps.

b) Storage array port is 2gbps, switch is 4gbps, HBA is 4 gbps.

c) Storage array port is 4 gbps, switch is 2 gbps, HBA is 4 gbps.

d) Storage array is 4 gbps, switch is 2gbps, HBA is 2gbps.

e) Storage array is 2gbps, switch is 2gbps, HBA is 4gbps.

f) Storage array is 2gbps, switch is 4gbps, Hba is 2gbps.

2) If a 4gbps E-port is connected to a 2gbps E-port what is the ISL speed?.

Please help me out with this. I always get confused with this.

I appreciate all your help.

[Torsten.]

All connections will do autoneg, unless they are set to fixed speed.

2a) array - switch 4GB; switch server 2GB

...

see 2a)

All are point to point; each point to point will be autoneg'd (highest possible speed).

[white221g]

All mentioned speeds are my question are the maximum possible speeds and autonegotiate is enabled on all ports. Please answer explaining why for each case. Appreciate your help.

[Torsten. · Accepted solution]

It is always

server - switch at max

switch - array at max


if it is fabric point to point.

[Torsten.]

2a) 4-4(2)-2
2b) 2-2(4)-4
2c) 2-2-2
2d) 2-2-2
2e) 2-2-2
2f) 2-2-2

[white221g]

Do you mean to say:
1) If Storage array port max speed is higher than than switch port max speed, both will work at switch port max speed.

2) If HBA max speed is higher than Switch port max speed, both will work at switch port max speed.

3) If switch port max speed is 2 gbps and storage array port max speed is 4 gbps and HBA max speed is 4gbps, array port and HBA will work at max 2gbps.

4) If 4gb E port from one switch is connected to 2gb E port from other switch, ISL will work at max 2gb.

[Mark Wibaux]

As previous poster has stated, It's a point-to-point connection for each individual physical link. The individual links will negotiate to the highest common speed that both ends can handle.
Unless you hook your HBA directly to the array then a speed difference between the Storage array and the HBA will not be a consideration.

So for example with current hardware EVA4400 (host ports are 4Gb) to SAN Switch 8/8 SAN switch (switch ports are 8Gb) to 8Gb Qlogic HBA (ports are 8Gb).

- array (4Gb) to switch (8Gb) link will be 4Gb
- hba (8Gb) to switch (8Gb) link will be 8Gb

If you then had an older switch (SAN Switch 4/8) that you included in to the fabric
switch (8Gb) to switch (4Gb) link will be 4Gb

It's no different to a LAN, you can have a gigabit switch that has both gigabit and 10/100 NICs (or other switches) attached to it. Those links that are gigabit at both ends will negotiate to the highest speed. Those that have 10/100 at one end will only negotiate to a maximum of 100Mb.

[Torsten.]

Thank you Mark, I hope it is clear now.

[white221g]

Thank you. It is clear now. Appreciate all your help.