老路由openwrt升级到最新版，结果装samba提示/overlay空间不足

按照网上教程，改了/etc/opkg.conf，添加了一行：
dest usb /mnt/sda1/openwrt

也改了/etc/profile，添加了搜索路径

甚至安装时加上了-d，仍然不行：
root@OpenWrt:/mnt/sda1/openwrt#  opkg install -d usb samba4-libs
Installing samba4-libs (4.14.7-1) to root...
Collected errors:
* verify_pkg_installable: Only have 5092kb available on filesystem /overlay, pkg samba4-libs needs 7009
* opkg_install_cmd: Cannot install package samba4-libs.
root@OpenWrt:/mnt/sda1/openwrt#

不知该怎么弄？
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FROM 43.224.44.*