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http://www.freebsd.org/doc/en/books/handbook/mount-unmount.html

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http://www.freebsd.org/cgi/man.cgi?fstab(5)
http://daemonforums.org/showthread.php?t=4378


[b]FFS Mount Types[/b]

Unlike Windows filesystems, FreeBSD treats FFS partitions differently
depending on how they’re mounted. The manner in which a partition is
mounted is called the mount type. If you’re mounting a partition manually,
you can specify mount options on the command line, but if you’re using
/etc/fstab to mount it, you must specify any choice in the Options column.
Use -o mounttype to specify a mount type on the command line, or specify
the option in /etc/fstab in the Options column.
[b]Read-Only Mounts[/b]
If you want to look at the contents of a disk but not write to it, mount the
partition read-only. In most cases, this is the safest and the most useless way
to mount a disk, because you cannot alter the data on the disk or write any
new data.
Many system administrators mount the root partition, and perhaps even
/usr, as read-only to minimize potential system damage from a loss of power
or software problems. Even if you lose the physical hard drive due to a power
surge or other hardware failure, the data on the platters remains intact.
That’s the advantage of read-only mounts. The disadvantage is that system
maintenance becomes much more difficult because you cannot write to read-
only disks!
Read-only mounts are especially valuable when your computer is
damaged. While FreeBSD won’t let you perform a standard read-write
mount on a damaged or dirty filesystem, it can perform a read-only mount
most of the time. This gives you a chance to recover data from a dying system.
To mount a filesystem read-only, use one of the options rdonly or ro.
Both work identically.
[b]Synchronous Mounts[/b]
Synchronous (or sync) mounts are the old-fashioned way of mounting file-
systems. When you write to a synchronously mounted disk, the kernel waits
to see whether the write is actually completed before informing the program.
If the write did not complete successfully, the program can choose to act
accordingly.
Synchronous mounts provide the greatest data integrity in the case of a
crash, but they are also slow. Admittedly, “slow” is relative today, when even a
cheap disk outperforms what was the high end several years ago. Consider
using synchronous mounting when you wish to be truly pedantic on data
integrity, but in almost all cases it’s an overkill.
To mount a partition synchronously, use the option sync.
[b]Asynchronous Mounts[/b]
While asynchronous mounts are pretty much supplanted by soft updates,
you’ll still hear about them. For faster data access at higher risk, mount your
partitions asynchronously. When a disk is asynchronously mounted, the kernel
writes data to the disk and tells the writing program that the write succeeded
without waiting for the disk to confirm that the data was actually written.
Asynchronous mounting is fine on disposable machines, but don’t use it with
important data. The performance difference between asynchronous mounts
and noasync with soft updates is very small.
To mount a partition asynchronously, use the option async.
[b]Noasync Mounts[/b]
Finally, we have a method that combines sync and async mounts, called
noasync. This is FreeBSD’s default. When using noasync mounts, data that
affects inodes is written to the disk synchronously, while actual data is handled
asynchronously. Combined with soft updates (see later in this chapter), a
noasync mount creates a very robust filesystem.
Noasync mounts are the default, and you don’t need to specify anything.[/quote]
[b]FFS Mount Options[/b]

FreeBSD supports several mount options in addition to the mount types.
These options change the behavior of mounted filesystems.
[b]noatime[/b]
Every file in FFS includes an access-time stamp, called the atime, which
records when the file was last accessed. If you have a large number of files
and don’t need this data, you can mount the disk noatime so that FFS does
not update this timestamp. This is most useful for flash media or disks that
suffer from heavy load, such as Usenet news spool drives.
[b]noexec[/b]
The noexec mount option prevents any binaries from being executed on this
partition. Mounting /home noexec can help prevent users from running their
own programs, but for it to be effective, be sure to also mount /tmp, /var/tmp,
and anywhere else users can write their own files noexec as well. Also note
that a noexec mount doesn’t prevent a user from running a shell script,
which is just a set of instructions for a program elsewhere in the system.
Another common use for a noexec mount is when you have on your server
binaries for a different operating system or a different hardware architecture
and you don’t want anyone to execute them.
[b]nosuid[/b]
The nosuid option prevents setuid programs from running on your system.
Setuid programs allow users to run programs as if they’re another user. For
example, programs such as login(1) must perform actions as root but must
be run by regular users. Setuid programs obviously must be written carefully
so that intruders cannot exploit them to get unauthorized access to your
system. Many system administrators habitually disable all unneeded setuid
programs. You can use nosuid to disable setuid programs on a partition, but
script wrappers like suidperl get around this.
[b]nosymfollow[/b]
The nosymfollow option disables symlinks, or aliases to files. Symlinks are
mainly used to create aliases to files that reside on other partitions. To create
an alias to another file on the same partition, use a regular link instead. See
ln(1) for a discussion of links.
Aliases to directories are always symlinks; you cannot use a hard link
for that.[/quote]
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