ext2
The oldest Linux filesystem still viable for use now—ext2, does not have any journaling available. Therefore, any system that uses it is vulnerable to long fsck recovery times after a crash, which makes it unsuitable for many purposes. You should not put a database volume on ext2. While that might work theoretically, there are many known situations, such as any user error made during the quite complicated fsck process, this can break the write ordering guarantees expected by the database.
Because not journaling any writes is faster, ext2 volumes are used sometimes for PostgreSQL WAL volumes, which require very little in the way of data guarantees. Also, WAL volumes tend to be small filesystems without many files on them, and thus fairly quick to run fsck on. However, this does introduce the likely possibility of a failing automatic fsck check on reboot after a crash. This requires user intervention, and therefore, will make the server fail to start fully.
Rather than presuming...
