NFSD hang

[Kirill Yelizarov]

Good Day!
I'v got a problem with nfs share on zfs volume. Everything worked fine for a few month and now it hang. This share stores logs from 9 servers at night, about 1-2Gb from each server. ZFS is filled to 26% and it is v28

last pid: 46573;  load averages: 195.82, 199.86, 200.12                                                                               up 108+21:56:50 10:05:06
432 processes: 208 running, 224 sleeping
CPU:  0.0% user,  0.0% nice,  100% system,  0.0% interrupt,  0.0% idle
Mem: 280M Active, 1469M Inact, 9584M Wired, 161M Cache, 1232M Buf, 311M Free
Swap: 16G Total, 16G Free

  PID USERNAME      THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
 1666 root          256  76    0  5788K  5120K RUN    14 476.8H 1508.64% nfsd

# zpool list
NAME   SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
data  3.62T   954G  2.69T    25%  1.00x  ONLINE  -

# zfs list
NAME   USED  AVAIL  REFER  MOUNTPOINT
data   954G  2.64T   954G  /data

# zfs mount
data                            /data

What should i look for to resolve it?
Regards,
Kirill