What is xfsaild?

xfsaild is creating tons of system threads and blocking all the user processes. Both the user space as well as the kernel space threads report "INFO: task xfsaild /tdb:12345 blocked for more than 120 seconds. I'm not sure if this is related, but we just had this happen on one of our machines today - a task became blocked by xfsaild, and logins to the. When this happens, xfsaild only does reads (according to >> iotop) and consistently in D State (according to top). noticed that the load was consistenly at around 4, even with no obvious activity.