Extent Mapping Scheme for Flash Memory Devices

Abstract—Flash memory devices commonly rely on traditional address mapping schemes such as page mapping, block mapping or a hybrid of the two. Page mapping is more flexible than block mapping or hybrid mapping without being restricted by block boundaries. However, its mappingtable tends to grow large quicklyasthecapacityofflashmemorydevicesdoes.Toovercome this limitation, we propose a novel mapping scheme that is fundamentally different from the existing mapping strategies. We call this new scheme Virtual Extent Trie (VET), as it manages mapping information by treating each I/O request as an extent and by using extents as basic mapping units rather than pages or blocks. By storing extents instead of individual addresses, VET consumes much less memory to store mapping information and still remains as flexible as page mapping. We observed in our experiments that VET reduced memory consumption by up to an order of magnitude in comparison with the traditional mapping schemes for several real world workloads. The VET scheme also scaledwellwithincreasingaddressspacesbysyntheticworkloads. With a binary search mechanism, VET limits the mapping time to O(loglog|U|), where U denotes the set of all possible logical addresses. Though the asymptotic mapping cost of VET is higher than the O(1) time of a page mapping scheme, the amount of increased overhead was almost negligible or low enough to be hidden by an accompanying I/O operation. I