simple stripe set-up.
performance translators on the client side are 
writ-behind and io-cache

when dbench is run on this set-up
it crashes with the following core.

(gdb) bt
#0  0x00002aaaac32cfd4 in __wb_collapse_write_bufs (
    requests=0x2aaab40a44f8, page_size=131072) at write-behind.c:1354
#1  0x00002aaaac32dc68 in wb_process_queue (frame=0x69a4f0,
    file=0x2aaab40a44c0, flush_all=0 '\0') at write-behind.c:1435
#2  0x00002aaaac32e0b3 in wb_ffr_cbk (frame=0x69a4f0,
    cookie=<value optimized out>, this=<value optimized out>, op_ret=0,
    op_errno=0) at write-behind.c:1694
#3  0x00002aaaac1258a8 in stripe_stack_unwind_cbk (frame=0x69a580,
    cookie=0x6c6ca0, this=0x60f4c0, op_ret=0, op_errno=0) at stripe.c:231
#4  0x00002aaaabf06f67 in client_flush_cbk (frame=0x6c6ca0,
    hdr=0x2aaab4044440, hdrlen=<value optimized out>,
    iobuf=<value optimized out>) at client-protocol.c:4748
#5  0x00002aaaabf067da in protocol_client_pollin (this=0x60e010,
    trans=0x612c70) at client-protocol.c:6344
#6  0x00002aaaabf0d3a2 in notify (this=0x2aaab40a44f8, event=2,
    data=0x612c70) at client-protocol.c:6387
#7  0x00002aaaacd90d13 in socket_event_handler (fd=<value optimized out>,
    idx=0, data=0x612c70, poll_in=1, poll_out=0, poll_err=0) at socket.c:814
#8  0x00002aaaaacee2c5 in event_dispatch_epoll (event_pool=0x609840)
    at event.c:804
#9  0x0000000000403e0e in main (argc=6, argv=0x7fff0a37a0b8)
    at glusterfsd.c:1325
(gdb) fr 0
#0  0x00002aaaac32cfd4 in __wb_collapse_write_bufs (
    requests=0x2aaab40a44f8, page_size=131072) at write-behind.c:1354
1354                    if ((request->stub->fop != GF_FOP_WRITE)
(gdb) p request->stub
$4 = (call_stub_t *) 0x0
(gdb)

PATCH: http://patches.gluster.com/patch/1484 in master (performance/write-behind: Add a NULL check for request->stub before checking request->stub->fop.)

PATCH: http://patches.gluster.com/patch/1483 in release-2.0 (performance/write-behind: Add a NULL check for request->stub before checking request->stub->fop.)