Sometimes the default formatting options aren’t what you need, so i’ll explain a few of them here.
soft-updates are enabled with the -U option. Soft updates are generally a good idea, but you might run into problems if you enable them on a smaller partition as it can fill up before the system has had time to release free space to the user.
block size, frag size and inode size can be useful to change depending on your intended data usage. A single file will always use a minimum of the block size. If your intended data is likely to be a lot of small files (e.g. a maildir dump disk), then a 64kb block size is insane as a 100byte file will occupy 64kb of disk storage. inodes can be exhausted if your intended data is likely to be a lot of files. e.g. if your disk is likely to contain a few thousand large zip files then you need fewer inodes which frees up space for data.
for a disk that needs a lot of small files, i would go for something like:
newfs -O2 -U -b 4096 -f 512 -i 2048 /dev/da0s1a
for a disk that needs fewer files but generally has large files, you could increase the block and inode size:
newfs -O2 -U -b 65536 -f 8192 -i 65536 /dev/da0s1a
The defaults (at least in FreeBSD 7) are…
newfs -O2 -U -b 16384 -f 2048 -i 2048 /dev/da0s1a