A fundamental vision driving pervasive computing research is access to personal and shared data anywhere at anytime. In many ways, this vision is close to being realized. Wireless networks such as 802.11 offer connectivity to small, mobile devices. Portable storage, such as mobile disks and USB keychains, let users carry several gigabytes of data in their pockets. Yet, at least three substantial barriers to pervasive data access remain. First, power-hungry network and storage devices tax the limited battery capacity of mobile computers. Second, the danger of viewing stale data or making inconsistent updates grows as objects are replicated across more computers and portable storage devices. Third, mobile data access performance can suffer due to variable storage access times caused by dynamic power management,mobility, and use of heterogeneous storage devices. To overcome these barriers, we have built a new distributed ﬁle system called BlueFS. Compared to the Coda ﬁle system, BlueFS reduces ﬁle system energy usage by up to 55% and provides up to 3 times faster access to data replicated on portable storage.