I noticed the Pogoplug v2 / DockStar install guides (and maybe others) were updated and was surprised to see
an Ext4 filesystem being created on the USB drive and mounted. However the Pogoplug Linux Kernel has no support for Ext4:
$this->bbcode_second_pass_code('', '
Pogoplug:/tmp$ mount /dev/sda1 alarm
mount: mounting /dev/sda1 on alarm failed: Invalid argument
Pogoplug:/tmp$ dmesg|tail -n1
[ 312.890000] EXT2-fs: sda1: couldn't mount because of unsupported optional features (240).
')
Applying -t ext3 also fails due to Ext4's extended features set by default.
$this->bbcode_second_pass_code('', '
[root@linux ~]# tune2fs -l /dev/sdb1 | grep features
Filesystem features: has_journal ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
')
Edit: Issue was fixed.