Deleting vbuckets from disk is very slow.

Using 1.6.0beta3-2, from Sharon...

Lowered my default bucket RAM quota to 200M. Disk is 2G.
Loaded the system. First rebalancing was fine.
Now memcached is stuck at 100% cpu on 10.1.4.25. Steve is looking at it now.

1. pstack 15006
   Thread 10 (Thread 0x40f8c940 (LWP 15016)):
   #0 0x0000003355ec5f3b in read () from /lib64/libc.so.6
   #1 0x0000003355e6cc07 in _IO_new_file_underflow () from /lib64/libc.so.6
   #2 0x0000003355e6d5ce in _IO_default_uflow_internal () from /lib64/libc.so.6
   #3 0x0000003355e68e8b in getc () from /lib64/libc.so.6
   #4 0x00002b0309284898 in ?? ()
   #5 0x0000000000000000 in ?? ()
   Thread 9 (Thread 0x4198d940 (LWP 15017)):
   #0 0x0000003355e9a0b1 in nanosleep () from /lib64/libc.so.6
   #1 0x0000003355e99ed4 in sleep () from /lib64/libc.so.6
   #2 0x000000000041319b in check_isasl_db_thread ()
   #3 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #4 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 8 (Thread 0x4238e940 (LWP 15018)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x0000000000411f54 in worker_libevent ()
   #4 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #5 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 7 (Thread 0x42d8f940 (LWP 15019)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x0000000000411f54 in worker_libevent ()
   #4 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #5 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 6 (Thread 0x43790940 (LWP 15020)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x0000000000411f54 in worker_libevent ()
   #4 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #5 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 5 (Thread 0x44191940 (LWP 15021)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x0000000000411f54 in worker_libevent ()
   #4 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #5 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 4 (Thread 0x44b92940 (LWP 15022)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x0000000000411f54 in worker_libevent ()
   #4 0x0000003356a064a7 in start_thread () from /lib64/libpthread.so.0
   #5 0x0000003355ed3c2d in clone () from /lib64/libc.so.6
   Thread 3 (Thread 0x45593940 (LWP 15024)):
   #0 0x00002aaaaad1f17b in ?? ()
   #1 0x000000001d34682c in ?? ()
   #2 0x00002aaaaad06abe in ?? ()
   #3 0x0000000000000000 in ?? ()
   Thread 2 (Thread 0x45f94940 (LWP 15025)):
   #0 0x0000003356a0ae00 in pthread_cond_timedwait@@GLIBC_2.3.2 ()
   #1 0x00002aaaaacf1480 in ?? ()
   #2 0x4069000000000000 in ?? ()
   #3 0x0000000000000000 in ?? ()
   Thread 1 (Thread 0x2b0309283620 (LWP 15006)):
   #0 0x0000003355ed4018 in epoll_wait () from /lib64/libc.so.6
   #1 0x0000000000417950 in epoll_dispatch ()
   #2 0x0000000000415e81 in event_base_loop ()
   #3 0x000000000040ff1d in main ()

[root@Config131VM0 ~]# /opt/NorthScale/bin/ep_engine/management/stats.py 127.0.0.1:11210 all
auth_cmds: 1058
auth_errors: 0
bucket_conns: 14
bytes_read: 436821603
bytes_written: 100975398
cas_badval: 0
cas_hits: 0
cas_misses: 0
cmd_flush: 0
cmd_get: 39143
cmd_set: 325098
conn_yields: 713
connection_structures: 541
curr_connections: 24
curr_items: 59045
daemon_connections: 10
decr_hits: 0
decr_misses: 0
delete_hits: 0
delete_misses: 0
ep_bg_fetched: 12627
ep_bg_load_avg: 110 usec
ep_bg_max_load: 9078 usec
ep_bg_max_wait: 1222 ms
ep_bg_min_load: 25 usec
ep_bg_min_wait: 8 usec
ep_bg_num_samples: 12627
ep_bg_wait_avg: 1930 usec
ep_commit_time: 1
ep_data_age: 381
ep_data_age_highwat: 460
ep_dbinit: 0
ep_dbname: /opt/NorthScale/1.6.0beta3/data/ns_1/default
ep_flush_duration: 348
ep_flush_duration_highwat: 348
ep_flusher_state: running
ep_flusher_todo: 5124
ep_io_num_read: 82367
ep_io_num_write: 135452
ep_io_read_bytes: 169622735
ep_io_write_bytes: 260920172
ep_item_commit_failed: 0
ep_item_flush_failed: 0
ep_kv_size: 77408964
ep_max_data_size: 209715200
ep_max_txn_size: 50000
ep_mem_high_wat: 157286400
ep_mem_low_wat: 125829120
ep_min_data_age: 0
ep_num_eject_failures: 78252
ep_num_non_resident: 92889
ep_num_pager_runs: 5
ep_num_value_ejects: 105515
ep_oom_errors: 50045
ep_overhead: 25930136
ep_pending_ops: 0
ep_pending_ops_max: 1
ep_pending_ops_max_duration: 233 s
ep_pending_ops_total: 4
ep_queue_age_cap: 900
ep_queue_size: 0
ep_storage_age: 479
ep_storage_age_highwat: 479
ep_storage_type: featured
ep_tap_keepalive: 0
ep_too_old: 0
ep_too_young: 0
ep_total_cache_size: 267384710
ep_total_enqueued: 149866
ep_total_persisted: 139875
ep_version: 1.6.0beta3_9_gcafeba5
ep_warmed_up: 0
ep_warmup: true
ep_warmup_thread: complete
ep_warmup_time: 0
get_hits: 39143
get_misses: 0
incr_hits: 0
incr_misses: 0
libevent: 1.4.13-stable
limit_maxbytes: 67108864
mem_used: 103339100
pid: 15006
pointer_size: 64
rejected_conns: 0
rusage_system: 254.338334
rusage_user: 275.270152
tap_connect_received: 513
tap_mutation_received: 65242
tap_mutation_sent: 299188
tap_vbucket_set_received: 1024
tap_vbucket_set_sent: 1024
threads: 4
time: 1283356124
total_connections: 1071
uptime: 1117
version: 1.4.4_276_gff52fc9