SGI machines had capacitor banks in the power supplies large enough to power the machine long enough for the kernel interrupt handler to park all of the hard dr

SGI machines had capacitor banks in the power supplies large enough to power the machine long enough for the kernel interrupt handler to park all of the hard drive write heads. It turns out that the voltage required to keep the write head writing is often less than the voltage required to keep RAM from corrupting. At least for a time, XFS journaling correctness relied on the kernel being able to prevent garbage writes on loss of power. There used to be big caveats to using XFS on non-SGI hardware. Though, I think those caveats were roughly "XFS guarantees aren't much better than ext3/ext4 guarantees on power loss, on non-SGI hardware".