Because of delayed allocation and other performance optimizations, ext4's behavior of writing files to disk is different from ext3. In ext4, when a program writes to the file system, it is not guaranteed to be on-disk unless the program issues an fsync() call afterwards.

By default, ext3 automatically forces newly created files to disk almost immediately even without fsync(). This behavior hid bugs in programs that did not use fsync() to ensure that written data was on-disk. The ext4 file system, on the other hand, often waits several seconds to write out changes to disk, allowing it to combine and reorder writes for better disk performance than ext3.

If you are looking for running Connect in virtual machine with thin provisioned drives, you should go with XFS. Ext4 has an issue with not reusing free space.

If you use thick provisioning or physical drives, there's no really big difference between XFS and ext4 regarding performance (except fsck - thats' painfully slow for ext filesystems, really fast for XFS).

Also XFS native snapshots you might find useful.