[Dovecot] still problem with load

Farkas Levente lfarkas at bnap.hu
Wed May 21 11:58:25 EEST 2003

we've got (and getting more) serious problem with load. I'm just 
calculate that ther is about 300 mailbox with 20Gb mails. and the whole 
system is _very_ slow and just getting slower and slower. it's a fast 
lan every client has 100Mb connection to the server with gigabit crad 
and gigabit switches. when I push the delete button in a mail I usualy 
have to wait 10,20 or 30 seconds (!!!) to deleted and show me the next 
one. dovecot eat so much io to the hard disk, that we can't do too much.
currently at the same time about 100 clients are connected mostly with 
OE6. the server is a P4 server with 1GB ram and about 1TB hard disk. 
there is only one samba and dovecot on the server. and the load use to 
be something like this:
  10:47:38  up 3 days, 15:48,  2 users,  load average: 4.64, 3.58, 3.43
230 processes: 225 sleeping, 5 running, 0 zombie, 0 stopped
CPU states:   6.3% user   8.9% system   0.0% nice   0.0% iowait  84.6% idle
Mem:  1022840k av, 1013588k used,    9252k free,       0k shrd,   80320k 
                     826372k actv,   47324k in_d,   16904k in_c
Swap: 4193608k av,   80612k used, 4112996k free                  783088k 
as you can see it use almost all ram (as the 2.4 kernmel used to do) but 
no cache. so the ram is enough. the more interesting part is the load 
while the idle usualy between 80-90% the whole system doesn't use any 
cpu (or just minimal). BUT at the same time the load is around 3,4,5 
(!!!) which is too much, and more than acceptable. what's worse the 
reason is the io load on the hard disks. every process are waiting for 
io. in this case I usualy
service dovecot stop
killall imap
<wait about one minutes>
service dovecot start
and the load goes back to 0.3-0.6. after an hour the same happend and I 
have to do the same.:-((( what's more in this case samba case that all 
(!!!) clients stops for a few seconds. since everybody use OE6 they 
always download all messages with huge mailboxes what's more dovecot 
index the whole system all the time. I assume this cause the load. IMHO 
300 mailbox and 100 concurrent user is not such a big thing.
is there any way to restrict dovecot not to use so much io?
thanks in advance.

   Levente                               "Si vis pacem para bellum!"

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