LVM snapshots sometimes cause system hang
The system sometimes becomes unresponsive when using LVM snapshots and when file system blocks are not aligned on snapshot chunk boundaries. This is caused by a complex interaction between Device Mapper snapshots and per-process bio queuing, which might lead to a cyclic dependency and deadlock.
If you are affected by this problem, please upgrade to Red Hat Enterprise Linux 7, which fixes the deadlock. The fix is too invasive to be included in Red Hat Enterprise Linux 6 at this production phase. (BZ#1073220)