difference between filesystem and mountpoint

[bullz]

HI All,

Very silly question.

What is the difference between filesystem and mountpoint, where do we exactly use the term called “Filesystem” and “Mountpoint”.

* points will be shared at the end without fail.

[Matti_Kurkela]

In abstract sense, a filesystem is "something that has a capacity to hold files and directories". A filesystem might be contained in a disk partition (e.g. /dev/sda1), in a LVM logical volume (/dev/vg00/lvol1) or in a CDROM/DVD (/dev/scd0).

The "root filesystem" is a bit special: it is mounted at the system's root directory (/), and it is usually mounted very early in the system's boot sequence. You usually cannot unmount the root filesystem: if you could do that for some reason, you could not do anything but a system halt/reboot after that.

A mount point is the location where a filesystem's root directory is (or will be) attached to the system's directory hierarchy. The mount point of the root filesystem is always the root directory, /.

Any directory in any filesystem can serve as a mount point for mounting another filesystem: no special preparation is required.

The root directory of the "child" filesystem will overlap the directory of the "parent" filesystem that is used as a mount point. If the mount point directory on the "parent" filesystem contains files, those files will be inaccessible while the "child" filesystem is mounted. (Unless those files are hard-linked to some other location on the parent filesystem... but I digress.)

Unix/Linux sysadmins often talk about filesystems and their mountpoints somewhat interchangeably: for example, "the /usr filesystem" is a shorthand for "the filesystem that is normally mounted at mount point /usr".

Fundamental questions like this are interestingly tricky to answer: please ask for more explanations if I was unclear.

MK

[bullz]

Best explanation. +1

So, can I come to a conclusion that,

/dev/cciss/c0d0p3 3.0G 1.5G 1.4G 52% /usr
/dev/cciss/c0d1p1 133G 3.7G 122G 3% /data1

/usr mountpoint is 52% used.
/data1 mountpoint is 3% used.

Instead of referring it as filesystem?

only i suld use "Filesystem" when the communication related with /dev/cciss/c0d0p3 (or) /dev/cciss/c0d1p1

[Patrick Wallek]

>>So, can I come to a conclusion that,
>>/dev/cciss/c0d0p3 3.0G 1.5G 1.4G 52% /usr
>>/dev/cciss/c0d1p1 133G 3.7G 122G 3% /data1
>>/usr mountpoint is 52% used.
>>/data1 mountpoint is 3% used.
>>Instead of referring it as filesystem?

The best way, in my opinion, to state this would be: The filesystem on disk /dev/cciss/codop3, which is mounted to /usr, is 52% utilized.

It is the filesystem itself that contains the data. The mountpoint could change but where ever you mount it, it would be 52% utilized.

>>only i suld use "Filesystem" when the
>>communication related with /dev/cciss/c0d0p3 (or) /dev/cciss/c0d1p1

Not necessarily. Those are disk devices on which a filesystem has been created.

[Steven Schweda]

> /data1 mountpoint is 3% used.

That would seem to be approximately backward.

ls -l /data1
ls -ld /data1
umount /data1
ls -l /data1
ls -ld /data1

"/data1" is a mount point. It's the point
(a directory in the "/" (root) file system)
where the file system on /dev/cciss/c0d1p1 is
normally mounted.

If you do that "umount" command, then
remember to:
mount /data1

A file system is where the files are stored.
A file system can have a capacity, so it
might be, say, 3% full.

A mount point is where a file system appears
in the great tree of file systems. By
itself, it's a directory. It has no
intrinsic capacity, so it can't get full.

[Hakki Aydin Ucar]

A file system is where the files are stored according to their formats compatible to structure such as in file sizes , inode manipulation, lv attidutes..

A mount point is the created access directory that is compatible for this FS

[Matti_Kurkela]

> The best way, in my opinion, to state this would be: The filesystem on disk /dev/cciss/codop3, which is mounted to /usr, is 52% utilized.

Patrick is demonstrating the most complete and technically accurate form here.

But in common sysadmin work, you typically think about the disk device <-> filesystem relations only when you're setting up the system or changing its disk configuration, or troubleshooting a disk problem. Otherwise, you usually won't need to think about it.

On the other hand, the filesystem <-> mountpoint relation is much more important in everyday use, since it is used to define file locations in a way that is immediately usable for users and application configurations.

Therefore, referring to filesystem by using the name of its mountpoint (e.g. "the /opt filesystem") is a very common and practical shorthand.

The operation to identify a disk device when given the mount point of its filesystem (or vice versa) should be trivial for all Unix sysadmins: just type "mount" and read the list. Or on Linux, use "cat /proc/mounts".

MK

[Steven E. Protter]

Shalom,

A file system sits on top of a mount point.

Thats how I keep it straight. Mount point is just a path.

file system resides elsewhere but is mounted on a mount point.

Examples:

I have a file system called mydata. It was allocated disk on a logical volume vg01/lvol1

It is mounted /dev/vg01/lvol1 /mydata

For some reason I don't like that

umount /mydata

mkdir /oradata
mount /dev/vg01/lvol1/oradata

Same data, same file system really, new mount point.

SEP

[bullz]

Thanx all for you kind help. please post if you have any other view.

[Steven Schweda]

> please post if you have any other view.

Please post a question if something is not
yet clear.

[Zinky · Accepted solution]

Matti's explanation is utmost correct. I use the same explanation in my crusade against proper technical terminologies and jargons in my site.


Filesystems are data structure or format that exist on top of addressable block or raw or even file devices. Among the most well known filesystems are the ext family on Linux, ufs on BSD and Solaris, vxfs from Veritas/Symantec for all platforms. There are many others in various forms of development.

Now in case you have heard of ZFS (w/c is stable and coming to Linux) and claim it to be a "filesystem" that needs a mount point -- he/she is half correct -- but I digress.

Filesystems need to be mapped or mounted to a directory (also called a mount point). A mount point need not be a top level directory.

Filesystems can be created and exist on top of:
1) a whole simple disk
/dev/sdb on /apache/logs type vxfs (rw)

2) a disk partition
/dev/sdc3 on /saplog type ext4 (rw)

3) an LVM logical volume
/dev/mapper/sapvg01-logvol01 on /saplog01 type vxfs (rw)

4) a VxVM volume
/dev/rdsk/sapdg02/data01 on /sapdata01 type ext3 (rw)

5) a multipathed disk
/dev/mapper/SAPDISK01 on /sapdata type vxfs (rw)

6) a raid device
/dev/cciss/c0d1p1 on /apache type ext3 (rw)

7) a prorietary device say from EMC (Powerpath) or IBM (SVC)
... don;t have it..

8) a loopback file device
/data/file.dsk on /mnt/c type ext3 (rw,loop=/dev/loop2)


So "mount point" and "filesystem" cannot be used interchangeably IMHO. The precise way of using and commnicating is:

say you have:

# df -k /apache/logs

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vgapache-logs 1Tb .5Tb .5Tb 50% /apache/logs

# mount |grep logs
/dev/mapper/vgapache-logs on /apache/logs type ext3 (rw)

You would communicate it this way and it will impress your boss (assuming he is technical):

The mount point /apache/logs is an ext3 filesystem that resides on a logical volume named logs that is carved out of an LVM Volume Group vg-apache. It has 50% occupancy.



Hope this helps.

[bullz]

@ Alzhy
Really itâ s time to say wowâ ¦

@ Steven Schweda
Got so much info.

Thanx all.

[bullz]

Thanx