Raspberry Pi based Hadoop cluster [closed]
It would be incredibly bad. Hadoop eats heap like an elephant. The default heap size is 1000 MB but pretty much everybody increases it. 256 MB of RAM will not get you far, after the GPU and operating system take their toll, you'd probably have to restrict Java to 128 MB and the smallest jobs will run out of heap.
The JVM is also very slow on ARM. Red Hat plans to work with Linaro to improve this by Red Hat Enterprise Linux 7, but don't expect to run Java server loads on ARM reasonably for a while.