Port Costs and the Home Server!

Posted January 20, 2010 by Patrick Kennedy in Client Tips

Most people who build custom home servers will be able to articulate the cost per GB (cost/GB) of their drives. Yet this is a somewhat outdated metric. The major cost consideration that a lot of people overlook is port costs. Simply put, this is the cost to connect a hard drive to the system. For normal computer users this is often in the sub-$5 per port since they have open SATA connectors on their motherboards and open spots in their case making the cost of adding a drive the cost of a SATA cable. Home servers are a different story all together. A quick audit of the Big WHS showed that my port costs were approximately $46/ port. Compared to the $70 going price of a 1TB drive, this can be a huge portion of costs and is certainly appropriate to add to the cost/GB  equation.

To calculate port costs, I used a simple equation:

(Cost of Controllers + Cost of Port Expanders + Cost of Enclosures + Cabling Cost) / (Number of Installed Drives)

To give two examples:

The Big WHS (Main Chassis): ($450 Areca 1680LP + $200 HP SAS Expander + $330 Norco RPC-4020 + $40 miscellaneous SAS cables) / 22 Drives = $1020 / 22 = $46.36 / port or per drive connected!

The Old WHS: ($375 Adaptec 31605 + $100 Norco RP-470 + $200 2x iStarUSA 5-in-3 backplanes + $80 IcyDock 3-in-2 backplane + $20 SAS cables) / 16 Drives = $765/16 = $47.81 / port or drive connected

Of course, and important factor here is how full your server is. If you build a server such as The Big WHS and only populate it with ten drives, you end up spending $1020 in sunk port costs for ten drives or $102/ drive! This is more expensive than most 1TB and 1.5TB drives when they are on sale today!

To be clear, these costs are not all-inclusive. One could ascribe the need for a larger power supply, and additional PCIe ports to the above and get a closer approximation of port costs, however that involves incremental cost determinations, and frankly, it is a lot of work for in all likelihood allocating $40 or less of costs.

Practically speaking, let’s assume $47/ port. $70/ 1TB drive, $105/ 1.5TB drive, and $150/ 2TB drive ($0.07/GB. $0.07/GB, and $0.075/GB respectively). One would normally assume the 1TB and 1.5TB drives are the most cost-effective since they are lower cost options. However, let’s say one wants a 12TiB or raw storage home server. That would be 12x 1TB drives, 8x 1.5TB drives, and 6x 2TB drives for a raw drive cost of $840, $840, and $900 respectively. Assuming a $47 per port cost, the total costs to add to a home server are $1404 (12x 1TB drives), $1216 (8x 1.5TB drives), and $1182 (6x 2TB drives).

A few considerations are worth mentioning here. First, it is very common to have six SATA ports on a motherboard, so if one did not use raid and used Windows Home Server drive extender/ duplication instead the effective port cost would be under $5/ port for SATA cables and the like. Some boards could support the 8x 1.5TB drives, and very few the 12x 1TB drives. Second, using a static raw capacity (12TiB in our case) of storage strongly favors smaller drives in the cost/ usable GB category. The quick reason here is that using raid 6 the 12x 1TB drives would yield 10TiB raw usable raid 6 capacity, the 8x 1.5TB drives would yield 9TiB raw usable capacity while the 2TB drives would only yield 8TiB raw usable raid 6 capacity. So the equation gets to be a bit more complex. I will write up something on that soon.

About the Author

Patrick Kennedy

Patrick has been running ServeTheHome since 2009 and covers a wide variety of home and small business IT topics. For his day job, Patrick is a management consultant focused in the technology industry and has worked with numerous large hardware and storage vendors in the Silicon Valley. The goal of STH is simply to help users find some information about basic server building blocks. If you have any helpful information please feel free to post on the forums.


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