An expert on filesystem development, T'so played a key role in developing Ext4, the current generation of the Linux kernel's standard filesystem. He was hired earlier this year by Google when the search giant was transitioning its server storage infrastructure from Ext2 to Ext4. He says that he didn't influence the decision to use Ext4 in Android, but provided some advice and guidance to the Android team after the decision was made.
Most Android devices currently use YAFFS, a lightweight filesystem that is optimized for flash storage and is commonly used in mobile and embedded devices. The problem with YAFFS, T'so explained in his blog entry, is that it is single-threaded and would likely "have been a bottleneck on dual-core systems." Concurrency will be important on next-generation Android devices that use multi-core ARM processors. We expect to see dual-core Android devices, including tablets, announced as early as CES.