I’ve mentioned before that we use USB external drives for transportation of data from our colocation facility to the office.  After struggling to find reliable devices, we finally settled on the Seagate FreeAgent 1TB drives.  They’ve served us quite well for over a year now.  But recently it’s been taking a very long time to copy our data.

It used to take about three and a half hours to copy data (a couple hundred gigabytes) from the server to the removable drive.  Recently it’s been taking on the order of 10 to 12 hours.  At first I thought it was another idiotic problem with caching, similar to the problem I had copying large files between servers, except this copy would eventually complete.  The odd thing was that when I started the copy it would proceed at the expected rate and at some point slow to a crawl.

So I wrote my own program that reads a gigabyte at a time from the local drive and then writes it to the USB device, timing each write operation.  Running locally (at the office), the program reported a steady 24 MB/sec write speed, and copied the entire file at that rate.  Run at the data center copying the same file, the program reported the same 24 MB/sec for the first 20 gigabytes or so.  Then it slowed to about 4 MB/sec.

That smacks of a thermal problem.  Either the drive electronics or the server’s USB port was overheating.  I quickly eliminated the server’s USB port as the problem by hooking up a different USB device and checking to see that the server could pass more than 50 gigabytes of data without trouble.

So the problem is with the FreeAgent drive.  If you spend a little time searching online, you’ll see that other people have experienced overheating problems with the FreeAgent drives.  And looking at the design, I can see why:  the only ventilation is at the bottom of the device where the electronics are.

The picture on the left, above, shows the drive as we typically would place it in the rack at the data center.  It sits on top of one of our servers.  The spot where it’s sitting is directly above one of the disk drives.  That spot is cool to the touch when I tested it yesterday.  Note, however, that you can’t see any ventilation holes.  Those are on the other side of the enclosure, as shown by the red arrow in the picture to the right.

Since air enters the cabinet from where I was standing taking this picture, and flows towards the back, mounting the drive as shown on the left doesn’t allow for very good airflow.  So yesterday I placed the drive in the cabinet as shown on the right.  Then I ran my test program.  I was able to write about 90 gigabytes before the drive slowed down.  I’m convinced now that it’s a thermal problem.

I don’t quite know where to go from here, though.  I think the first thing I’ll try is lifting the drive higher off the surface it’s sitting on.  That should allow for better airflow, and perhaps will be enough to keep the electronics cool.  (The problem, according to what I’ve found online, appears to be the USB to SATA conversion electronics at the base of the drive enclosure.)  If changing the drive location doesn’t solve the problem, I’ll have to find a different model of removable drive that has better ventilation or better heat tolerance.  Perhaps it’s time to visit Fry’s and see about buying an enclosure that’s designed for use in the warm environment of a server rack.