continuous stream of writes?

On an otherwise idle machine, I now see a continuous stream of writes to
disk. I've only noted this over the last couple of weeks but this will
not be welcome behaviour on an SSD ..

How do I find the source of these writes?


imb_at_toshi:/home/imb> iostat 10
       tty            ada0              cd0            pass0             cpu
 tin  tout  KB/t tps  MB/s   KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
   0   992 58.53 229 13.10   0.00   0  0.00   0.37   0  0.00  13  2  7  1 78
   0    23 30.82  12  0.36   0.00   0  0.00   0.00   0  0.00   2  0  4  0 94
   0     8 31.38  12  0.37   0.00   0  0.00   0.00   0  0.00   0  0  4  0 96
   0     8 31.75  11  0.34   0.00   0  0.00   0.00   0  0.00   3  0  3  0 94
   0     8 31.82  11  0.35   0.00   0  0.00   0.00   0  0.00   1  0  3  0 96
   0     8 31.76  12  0.36   0.00   0  0.00   0.00   0  0.00   0  0  3  0 96
   0     8 31.75  11  0.35   0.00   0  0.00   0.00   0  0.00   1  0  4  0 95
   0     8 31.55  12  0.38   0.00   0  0.00   0.00   0  0.00   1  0  3  0 96