wa (Waiting for I/O) from top command is high

遇到有台機器動作很慢， 用 top 一看，loading 滿重的， 而且 wa 高達 96.9%, 看起來應該是 io 出了問題

$ top
top - 03:08:30 up 34 days, 15:48,  1 user,  load average: 41.70, 43.33, 43.77
Tasks: 323 total,   1 running, 322 sleeping,   0 stopped,   0 zombie
Cpu(s):  1.4%us,  1.4%sy,  0.0%ni,  0.0%id, 96.9%wa,  0.0%hi,  0.3%si,  0.0%st
Mem:   1019112k total,   953076k used,    66036k free,     1092k buffers
Swap:  4111356k total,  2204620k used,  1906736k free,    22320k cached

http://serverfault.com/questions/155882/wa-waiting-for-i-o-from-top-command-is-big

$ iostat 1
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.03    0.00    1.03   97.94    0.00    0.00

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
scd0              0.00         0.00         0.00          0          0
sda             493.81      7327.84       738.14       7108        716
sdb               0.00         0.00         0.00          0          0