1. A computer-implemented method of accessing a data unit stored at a leaf node of a distributed index tree, the method comprising: using a reference from a superblock to access an available copy of a root node, copies of the root node stored on different devices among a plurality of storage devices, each copy of the root node comprising a first reference to a first copy of a branch of the distributed index tree and a second reference to a second copy of the branch, wherein the branch leads to one or more copies of a parent node; accessing, by a computer processor, an available copy of the parent node, copies of the parent node stored on different devices among the plurality of storage devices, each copy of the parent node comprising a first electronic reference to a first copy of a leaf node stored on a first storage device, a second electronic reference to a second copy of the leaf node stored on a second storage device, and a third electronic reference to a third copy of the leaf node stored on a third storage device, the first storage device different from the second storage device; determining, by a computer processor, that the first storage device is unavailable; based on the determination that the first storage device is unavailable, choosing to access the second copy of the child node instead of the third copy of the child node based on a technique including at least one of a round robin technique based on the last storage device used, selecting a most recently used storage device, and choosing based on a preference of local storage devices over remote storage devices; and processing, by a computer processor, the second electronic reference to access the second copy of the leaf node stored on the second storage device.