I've an x4540 Sun storage server running NexentaStor Enterprise. It's serving NFS over 10GbE CX4 for several VMWare vSphere hosts. There are 30 virtual machines running.

For the past few weeks, I've had random crashes spaced 10-14 days apart. This system used to open OpenSolaris and was stable in that arrangement. The crashes trigger the automated system recovery feature on the hardware, forcing a hard system reset.

Here's the output from mdb debugger:

panic[cpu5]/thread=ffffff003fefbc60: 
Deadlock: cycle in blocking chain


ffffff003fefb570 genunix:turnstile_block+795 ()
ffffff003fefb5d0 unix:mutex_vector_enter+261 ()
ffffff003fefb630 zfs:dbuf_find+5d ()
ffffff003fefb6c0 zfs:dbuf_hold_impl+59 ()
ffffff003fefb700 zfs:dbuf_hold+2e ()
ffffff003fefb780 zfs:dmu_buf_hold+8e ()
ffffff003fefb820 zfs:zap_lockdir+6d ()
ffffff003fefb8b0 zfs:zap_update+5b ()
ffffff003fefb930 zfs:zap_increment+9b ()
ffffff003fefb9b0 zfs:zap_increment_int+68 ()
ffffff003fefba10 zfs:do_userquota_update+8a ()
ffffff003fefba70 zfs:dmu_objset_do_userquota_updates+de ()
ffffff003fefbaf0 zfs:dsl_pool_sync+112 ()
ffffff003fefbba0 zfs:spa_sync+37b ()
ffffff003fefbc40 zfs:txg_sync_thread+247 ()
ffffff003fefbc50 unix:thread_start+8 ()

Any ideas what this means?