by NetApp A-Team Member Ryan Beaty, Infrastructure Practice Manager, Zumasys
ATTO Fibre Channel bridges vs. SAS optical transceivers
During a recent MetroCluster upgrade, I discovered that I needed ATTO Fibre Channel bridges. The 6500N ATTO Fibre Channel SAS bridges work great, but they’re pretty expensive. Being the ethical sales engineer that I am, I investigated NetApp’s SAS optical transceivers as an alternative.
The SAS optical transceivers are about half the cost of the ATTO bridges. They are also more time consuming and complicated to install. However, if you are dead set on using the SAS optical transceivers, let my experience be your guide. Use the diagrams in this blog to augment NetApp’s installation documentation.
Figure #1: SAS Optical Transceivers
However, the transceivers I purchased did not come with MPO cables, which meant I had to order some. NetApp offers an MPO to 4 x LC cable (part number X66008A-R6). Four LC fibre pairs are required for one SAS optical transceiver.
Figure 2: Part number and cable information
Next, I started rereading the documentation on the SAS optical transceivers. The documents state, “Requires eight patch panel ports per connection.” I understood that to mean eight patch panel ports per sycnronous stack, just like the MetroClusters using the older DS14 shelves: four ports on site A and four ports on site B.
But that raises the question, “Why would you need four ports per SAS optical transceiver at each site?” To achieve multipath HA, that would be four connections multiplied by four 4 x LC patch panel ports for a total of sixteen fibre pairs, or 160Gbps for one stack in each site of the MetroCluster. Most companies don’t have sixteen fibre pairs just lying around waiting for a few Gbps of bandwidth to travel through them.
Figure 3: Cabling diagram
Figure 4: MPO to 4 x LC SAS cables
I searched the internet and found a 5m cable for $99.50 from an online off-brand, which sounded like a great deal. I got a quote for what I thought were the same cables from NetApp. Each cable was around $3,000. That meant a total of eight cables would cost $24,000-the price of a shelf.
Even though I could buy the cables for cheap online, the big problem is that if I bought the non NetApp cables, I would risk losing support for the whole system. If I had an issue down the road, NetApp could easily run the part numbers on the cables and void support for the entire system.
I was ready to abandon the idea of SAS optical transceivers altogether. Either I risk losing support with off-brand SAS cables, or I go way over budget and purchase them from NetApp. Maybe the SAS optical transceivers weren’t the cheaper option after all? Then I had my “ah-ha” moment.
After doing more research on the NetApp SAS cables, I discovered why they were so expensive-they shipped with their own SAS optical transceivers. Because the NetApp documentation was unclear on how to purchase the necessary equipment to complete the installation, I had mistakenly ordered separate SAS optical transceivers. If I had purchased the SAS cables from NetApp to begin with, I would not have needed additional transceivers, and I would have saved myself a lot of time and money. Well, they say hindsight is 20-20.
My suggestion: Go with the ATTO bridges
Although the SAS optical transceivers are a cheaper option than the ATTO bridges, my recommendation is to go with the latter. The complicated installation and confusing purchasing documentation of the SAS optical transceivers are, in my opinion, not worth the cost savings. The requirement for fibre runs between the two sites is also something to consider. Most people don’t want to or cannot make the many optical runs required for SAS optical transceivers. However, if your customer is cost conscious and is willing to pay for the extra time it will take for you to set up the equipment, then the SAS optical transceivers may be the right option.