A system is described for providing more efficient ways to implement attachable writable volumes for capturing write data in virtual desktops. In particular, embodiments described herein leverage a local differencing virtual disk to which write data on a virtual machine is saved, and a background process for syncing the differencing virtual disk with an attachable master writable volume where user data is stored long-term. As a result, in cases where desktop performance would suffer due to limited data transfer speeds between the virtual machine and the master writable volume, the performance penalty caused by write delays is spared by writing the data first to the local differencing virtual disk, and then syncing the master writable volume with the differencing virtual disk in the background.