August 18, 2005

Putting together a new array

My birthday is coming up. I’m not sure if I have enough variety in my wish list, so I was thinking about putting a new disk array on there. My current 480GB array is at something like 91% full.

Naturally the first thing that comes to mind is SATA. Cheap and real fast. Of course, then I find out an interesting fact: most IDE drives can’t sustain more than about 70MB/s anyway. I had no idea, really. When they’re serving from cache, sure, they can do way faster than 70MB/s, but how big is your cache? 8MB? 16MB? I gather that cache, especially in a file server, isn’t terribly important.

Moreover, if you look at the reviews on you’ll see that almost every disk in the same capacity/RPM has almost the same performance. Hence lots of people in their forums telling you to look for best price or warranty, instead of performance numbers.

That was eye opening. Plus, it took away my requirement for PCI Express (henceforth PCIe). I figured I’m going to have 8-9 drives, 8 * 300MB/s (SATA II) = 2400 MB/s. I needed PCIe. All I was finding, though, were PCI-X controllers, 64-bit/133MHz at best. Very few people made PCIe controllers, especially with more than two SATA II ports–if SATA II at all. Now I realize, though, that I should plan for something more like 8 * 70MB/s = 560MB/s, which is well in the reach of 64-bit/133MHz PCI-X, which should work out to theoretical maximum throughput of about 1GB/s. That even leaves enough room for PCI-X gigabit NIC if I need one (i.e., if it’s not on-board).

My brain is awash with my research of the past couple days. I just realized I need to organize it a bit more, to present all the interesting products, sites, standards, and other information I found. So I’ll put off more information until a future (near future, hopefully) entry.

I’ll add just a couple more random things:

  • I’m almost positive I can put together 2TB and a new server for way, way less than I could do it from, say, Dell, HP, or IBM. I like IBM’s server web site the best, though, especially their server finder. This may drive me to buy from them in the future. (That and their prices and servers look pretty damn good.)
  • Linux SATA support still looks a bit shaky. Only a few chipsets, for example, seem to support hot swap, port multipliers, etc. All the interesting chipsets have bare minimum support, sometimes from the vendor, sometimes from the community. Here I’m talking about the SIL3124 (no PM, no hot swap, according to comments in the latest libata patches) and Areca/Tekram (Marvell?) cards especially. I’ll talk more about them later, but if you want an SATA expansion card with good Linux support, my initial findings suggest you’re best off going with 3ware who release their own drivers which seem to be subsequently included in the kernel.

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