"Leaking" disk space on FreeBSD servers

    > grep /usr/local/pgsql /etc/fstab
    /dev/mfid1s1d   /usr/local/pgsql    ufs   rw   2   2

    > tunefs -p /usr/local/pgsql/
    tunefs: POSIX.1e ACLs: (-a)                                disabled
    tunefs: NFSv4 ACLs: (-N)                                   disabled
    tunefs: MAC multilabel: (-l)                               disabled
    tunefs: soft updates: (-n)                                 enabled
    tunefs: gjournal: (-J)                                     disabled
    tunefs: trim: (-t)                                         disabled
    tunefs: maximum blocks per file in a cylinder group: (-e)  2048
    tunefs: average file size: (-f)                            16384
    tunefs: average number of files in a directory: (-s)       64
    tunefs: minimum percentage of free space: (-m)             8%
    tunefs: optimization preference: (-o)                      time
    tunefs: volume label: (-L)                                

LSOF isn't showing any open files:

    > lsof +L /usr/local/pgsql/ | awk '{ print $8 }' | grep 0 | wc -l
    0

We're not creating filesystem snapshots:

    > find /usr/local/pgsql/ -flags snapshot
    >

Not all of our servers are leaking space, it's only the more recently-installed systems. Here's a quick breakdown of versions:

    FreeBSD   PostgreSQL   Leaking?
    8.0       8.4.4        no
    8.2       9.0.4        no
    8.3       9.1.4        yes
    8.3       9.2.3        yes
    9.1       9.2.3        yes

Each of these servers is configured with a warm standby, so we've been switching them over to the standby to reclaim the space (rebooting the primary is too much downtime). The standby does *not* demonstrate this problem while it's being used as a standby, but it starts leaking space once it's been made the primary.

Initially I thought this might be related to WAL files, however the pg_xlog dir is symlinked outside of the /usr/local/pgsql partition that is demonstrating this problem:

    > ll /usr/local/pgsql/data/pg_xlog    
    lrwxr-xr-x 25B Oct 19 10:48 pg_xlog -> /usr/local/pglog/pg_xlog/

I've exhausted everything I can think of to try to solve this one. Has anyone got any ideas on how to go about debugging this?

Thanks,

Dan