3-days-long vacuum of 20GB table

This autovacuum has been hammering my server with purely random i/o
for half a week. The table is only 20GB and the i/o subsystem is good
for 250MB/s sequential and a solid 5kiops. When should I expect it to
end (if ever)?

current_query: VACUUM reuters.value
query_start: 2008-04-15 20:12:48.806885-04
think=# select * from pg_class where relname = 'value';
-[ RECORD 1 ]--+---------------------------------
relname | value
relfilenode | 191425
relpages | 1643518
reltuples | 1.37203e+08
# find -name 191425\*
./16579/191425
./16579/191425.1
./16579/191425.10
./16579/191425.11
./16579/191425.12
./16579/191425.13
./16579/191425.14
./16579/191425.15
./16579/191425.16
./16579/191425.17
./16579/191425.18
./16579/191425.19
./16579/191425.2
./16579/191425.3
./16579/191425.4
./16579/191425.5
./16579/191425.6
./16579/191425.7
./16579/191425.8
./16579/191425.9
# vmstat 1
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 1 30336 46264 60 7882356 0 0 250 299 1 1 6 2 87 5
0 1 30336 47412 60 7881308 0 0 2896 48 944 4861 3 2 71 24
0 2 30336 46696 60 7882188 0 0 816 4 840 5019 1 0 75 24
0 1 30336 49228 60 7879868 0 0 1888 164 971 5687 1 1 74 24
0 1 30336 49688 60 7878916 0 0 2640 48 1047 5751 1 0 75 23
autovacuum | on
autovacuum_vacuum_cost_delay | -1
autovacuum_vacuum_cost_limit | -1
vacuum_cost_delay | 0
vacuum_cost_limit | 200
vacuum_cost_page_dirty | 20
vacuum_cost_page_hit | 1
vacuum_cost_page_miss | 10