Things to be aware of when migrating to 8 Gbps Fibre Channel
anthonyv 2000004B9K Visits (6820)
Its now becoming far more common to see 8 Gbps Fibre Channel switches and HBAs. IBM offer a very comprehensive range of 8 Gbps capable switches manufactured by both Brocade and Cisco. These range from top of the line SAN Directors like the IBM SAN768B (Brocade DCX) and the Cisco MDS9513 to 1U switches like the MDS9148 and the IBM SAN40B-4 (Brocade Silkworm 5100).
You can check them all out here: htt
Of course we should not forget 8 Gbps capable IBM BladeCenter modules from Brocade and Qlogic, which you can check out here:
The transition to 8 Gbps switches is not without some potential 'gotchas' which its worth being aware of.
1) The tyranny of distance
Its important to realise that as optical speeds increase, the effective distance that we can safely transmit these signals decreases. If your doing a drop and replace upgrade where existing fibres are moved from an older 1, 2 or 4 Gbps switch to a new 8 Gbps capable switch, if the link is now able to run at 8 Gbps, perhaps you may have unintentionally exceeded recommended cable lengths. These numbers for shortwave (850 nm) SFPs are sourced from an IBM Announcement letter, but I have seen some subtle differences between vendors, I suspect based on which SFPs are being used. The lesson to learn here is that as the speed of the link doubles, the recommended length of the cable decreases. If your 50 micron cables are 300 meters long, they will work well at 1 and 2 Gbps, but may well prove unreliable at 8 Gbps.
In the case of longwave SFPs (that operate at 1310 nm) I will write a second article because there are complicating factors due to the increasing use of extended distance SFPs.
2) Fillwords at 8 Gbps
I have received quite a few reports of clients having issues connecting DS5000s to Brocade switches running at 8 Gbps.
You can find this tip explaining how to diagnose and correct this issue on the IBM Support Site.
To check out details of why this happened, visit the release notes for Brocade FOS 6.2.0e firmware found here:
You should also have a read of these release notes for v6.3.0c that can be found at the same URL above.
These suggest that for the following devices at 8 Gbps, the fill words should be set to IDLE: