Change sugar upload dir to another disk/mount

.htaccess

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...

# file path will depend on the installation path or where the file should be
# if this needs to be executed everywhere (even from cron), consider setting it on php.ini instead of the .htaccess
php_value auto_prepend_file /var/www/html/sugar/prepend.php

config_override.php

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$sugar_config['upload_dir'] = '/my/external/upload';

prepend.php

<?php
define('SHADOW_INSTANCE_DIR', '/my/external/upload');

setupDir.sh

#!/bin/bash
# something similar to the commands below, based on the environment settings and apache user

mkdir -p /my/external/upload
chown -R www-data:www-data /my/external/upload
chmod -R 700 /my/external/upload