pg_xlog on a hot_stanby slave

Hi everyone,

Questions about pg_xlogs again...
I have two Postgresql 9.1 servers in a master/slave stream replication
(hot_standby).

Psql01 (master) is backuped with Barman and pg_xlogs is correctly
purged (archive_command is used).

Hower, Psql02 (slave) has a huge pg_xlog (951 files, 15G for 7 days
only, it keeps growing up until disk space is full). I have found
documentation and tutorials, mailing list, but I don't know what is
suitable for a Slave. Leads I've found :

- checkpoints
- archive_command
- archive_cleanup

Master postgresq.conf :

[...]
wal_level = 'hot_standby'
archive_mode = on
archive_command = 'rsync -az /var/lib/postgresql/9.1/main/pg_xlog/%f
barman(at)nas(dot)lan:/data/pgbarman/psql01/incoming/%f'
max_wal_senders = 5
wal_keep_segments = 64
autovacuum = on

Slave postgresql.conf :

[...]
wal_level = minimal
wal_keep_segments = 32
hot_standby = on

Slave recovery.conf :

standby_mode = 'on'
primary_conninfo = 'host=10.0.0.1 port=5400 user=postgres'
trigger_file = '/var/lib/postgresql/9.1/triggersql'
restore_command='cp /var/lib/postgresql/9.1/wal_archive/%f "%p"'
archive_cleanup_command =
'/usr/lib/postgresql/9.1/bin/pg_archivecleanup
/var/lib/postgresql/9.1/wal_archive/ %r'

How can I reduce the number of WAL files on the hot_stanby slave ?

Thanks

Regards.

Xavier C.