RAC

One of the biggest problems wih RAC is getting it installed. It’s not something I do often – which means it takes me far too long to do when I need to do it. But sometimes you’ve just got to go ahead and find the time. Three or four years ago I built myself a RAC stack – four nodes, because that’s the minimum number of sensibel testing.  (If you want to know why: two nodes is a very special case because you don’t have to worry about three-way negotiations; three nodes is a special case because if you’re testing failure scnerios then three nodes fails to two nodes – which is a special case. So four nodes is the smallest generic RAC installation – and that’s ignoring the question of standby systems, of course.)

My previous RAC stack, costing me about £2,000, is pictured is pictured on the left.

That’s four boxes I built from kits, an old laptop to do iSCSI emulation, and a spare 250GB external drive. I’ve got two routers there, one for the public network, one for the private; the boxes have 2GB of RAM and dual core pentium chips, and the O/S is Redhat. When I use it I tend to use Cygwin on my laptop and run up lots of telnet sessions. The system is very good for testing failures and node evictions because even with two big fans and a 4″ air gap (the white bits are polystyrene blocks) the third box down tends to overheat after about 45 minutes and crash – so most of the time I’m actually only using a three-node RAC.

Anyway, the reason for showing you this picture is because I’ve finally retired the old boxes and got some new kit. My new RAC stack,  costing only £1,600, is on the right. As you can see, it’s a laptop (if you’ve got a big lap).

It’s got 16GB of RAM, 2 x 500GB discs, and a 2nd generation i7 quad-core CPU which – according to Windows 7 Pro - is also capable of double-threading. I haven’t actually had time to set up the RAC system yet (I think I’ll have a couple of free days for that around the end of August), I’ve only got as far as installing a basic Linux virtual machine as the first step in the process. But for the photo I created four virtual Windows XP Pro machines under VMWare, then started  six Oracle instances across the four machines. The battery lasted about 90 minutes, but apart from that I think I’ve got a good indication that it will handle a four-node linux RAC with a windows Grid Control front-end if I want it to.

Footnote: Every time I buy some new kit (which is about once a year) I am stunned by the rate of change. My first PC cost me £2.300: it was an Apple II with the full 64KB of RAM, 2 x 360KB floppy disc drives (5.25″), 1MHz CPU (6502) and the special graphics card that allowed something like 320 x 250 pixels – and Visicalc was still faster than Excel on my latest laptop.