ProFTPD creates large send queue

[KamilL]

Hello,
I have a problem with my ProFTPD server. I have users with a very slow internet connection (8 MBit/s), if they start a transfer with FileZilla (10 simultaneous) I break the tcpsndbuf limit on my vServer at hosteurope and everything is working slower than slow.

I don't want to limit a maximum number of connections to my server but get a working configuration to not create such a huge send queue. Can anyone give me some hints?

/etc/proftpd.conf

ServerName                              "ProFTPD"
ServerType                              inetd
DefaultServer                           on

<Global>
        DefaultRoot                     ~
        AllowOverwrite                  on
</Global>

DefaultTransferMode                     binary
UseFtpUsers                             on

TimesGMT                                off
SetEnv TZ :/etc/localtime
Port                                    21

Umask                                   022

SocketOptions rcvbuf            8192
SocketOptions sndbuf            8192
CommandBufferSize               2048

ScoreboardFile /var/run/proftpd_scoreboard
TransferLog /opt/psa/var/log/xferlog

<Directory /var/www/vhosts>
        GroupOwner psacln
</Directory>

<Directory /home/*>
        GroupOwner psacln
        HideFiles ^\..*
</Directory>

<IfModule mod_xfer.c>
        TransferPriority APPE,RETR,STOR low
        AllowRetrieveRestart on
        AllowStoreRestart on
</IfModule>

<IfModule mod_tls.c>
        TLSEngine on
        TLSLog /var/log/tls.log
        TLSProtocol SSLv3 TLSv1

        TLSRequired off

        TLSRSACertificateFile /etc/ssl/private/proftpd.cert.pem
        TLSRSACertificateKeyFile /etc/ssl/private/proftpd.key.pem

        TLSVerifyClient off
        TLSRenegotiate none
        TLSCipherSuite ALL:!ADH
        TLSOptions NoSessionReuseRequired
</IfModule>

AuthPAM                 on
AuthPAMConfig           proftpd

IdentLookups            off
UseReverseDNS           off

AuthGroupFile           /etc/group

Include                 /etc/proftpd.include

/etc/xinetd.d/ftp_psa

service ftp
{
        flags           = IPv6
        disable         = no
        socket_type     = stream
        protocol        = tcp
        wait            = no
        user            = root
        instances       = UNLIMITED
        server          = /usr/sbin/in.proftpd
        server_args     = -c /etc/proftpd.conf
        nice            = 19
}

netstat -plant
LOCAL_IP = server ip address
REMOTE_IP = client ip address

Proto Recv-Q Send-Q Local Address       Foreign Address    State       PID/Program name
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65241    ESTABLISHED 1763/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65240    ESTABLISHED 1762/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65239    ESTABLISHED 1760/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65238    ESTABLISHED 1758/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65237    ESTABLISHED 1757/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65236    ESTABLISHED 1756/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65235    ESTABLISHED 1754/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65234    ESTABLISHED 1755/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65233    ESTABLISHED 1753/proftpd: damci
tcp        0      0 LOCAL_IP:21         REMOTE_IP:65232    ESTABLISHED 1752/proftpd: damci
tcp        0 351860 LOCAL_IP:46411      REMOTE_IP:65249    ESTABLISHED 1758/proftpd: damci
tcp        0 400040 LOCAL_IP:43561      REMOTE_IP:65248    ESTABLISHED 1762/proftpd: damci
tcp        0 346020 LOCAL_IP:43805      REMOTE_IP:65251    ESTABLISHED 1763/proftpd: damci
tcp        0 242360 LOCAL_IP:39351      REMOTE_IP:65244    ESTABLISHED 1760/proftpd: damci
tcp        0 164980 LOCAL_IP:56746      REMOTE_IP:65250    ESTABLISHED 1756/proftpd: damci
tcp        0 426320 LOCAL_IP:58194      REMOTE_IP:65247    ESTABLISHED 1753/proftpd: damci
tcp        0 246740 LOCAL_IP:50273      REMOTE_IP:65245    ESTABLISHED 1755/proftpd: damci
tcp        0 511000 LOCAL_IP:50823      REMOTE_IP:65246    ESTABLISHED 1757/proftpd: damci
tcp        0 245280 LOCAL_IP:51629      REMOTE_IP:65243    ESTABLISHED 1754/proftpd: damci
tcp        0 140160 LOCAL_IP:53504      REMOTE_IP:65242    ESTABLISHED 1752/proftpd: damci

/proc/user_beancounters

resource                     held              maxheld              barrier                limit              failcnt
tcpsndbuf                 9830824              9830824              9830400             13762560           1652656966

 

[KamilL]

No one has any idea how to prevent such large send queues?