Reconsidering external disk enclosures versus disk servers
Not even three months ago I confidently wrote about all of the good reasons why we were picking external disk enclosures over disk servers. Today I'm here to tell you why we've flip-flopped on that and are now planning to buy disk servers instead. What it boils down to is money.
(I could claim it was also uncertainties over SATA disks behind SAS expanders, but not really; I only started really reading about those issues after we'd made the decision.)
What started the ball rolling was that we found reasonably affordable motherboards with onboard dual 10G-T Ethernet ports (and SAS). These were pretty much the only affordable way of doing 10G in our next generation of fileserver hardware. However, going with this motherboard meant no more generic inexpensive servers; instead we'd have to specify out a case and all of the other things for it. This basically meant that we had a 'one chassis or two' choice; we could buy a case for the motherboard and then a second case as an external disk enclosure, or we could buy just one case and put both the motherboard and the disks into it. Using a single case will save us a significant amount per backend and it turned out that we could find a suitable case (in fact one with a near-ideal disk configuration).
I still believe in all of the merits of external disk enclosures that I wrote about in my original entry. But until we can get inexpensive generic servers with dual 10G-T (and SAS) all of them are trumped by budget practicalities. We can deal with the moderate downsides.
(There are also some upsides, such as fewer exterior cables to get snagged and accidentally yanked loose. I'm always a bit nervous when I'm behind our current fileserver racks because of all of the ESATA cables.)
(Would I still buy external disk enclosures if we had the budget for it? I'm honestly not sure. Those advantages are real but I'm not convinced that they're worth the cost, especially when compared to other things you could do with the same amount of money. If I had endless money, yes definitely; we'd use SAS disks in external SAS JBODs connected to generic servers with dual 10G-T onboard.)