Re: which files took the space
On Friday 04 March 2016 07:18:59 Adam Wilson wrote:
> On Fri, 4 Mar 2016 04:03:01 +1100 Andrew McGlashan
>
> <andrew.mcglashan@affinityvision.com.au> wrote:
> > On 4/03/2016 3:07 AM, Adam Wilson wrote:
> > > On Fri, 4 Mar 2016 03:03:53 +1100 Andrew McGlashan
> > >
> > > <andrew.mcglashan@affinityvision.com.au> wrote:
> > >> It also may have been files in the file system, but where another
> > >> file system mount hides them....
> > >
> > > What does this mean? Mounts overlapping and hiding other mounts?
> > >
> > > Explain, please.
> >
> > Yes, this is more likely to happen to the root file system.
> >
> > Say you have a bunch of files in /boot, but for some reason you have a
> > /boot partition that wasn't mounted when those files were created ....
> > then you mount the /normal/ boot partition over it and now the other
> > files are now hidden from view, but still taking up space.
>
> So you're talking about creating files in an unmounted partition, and
> then mounting it, but since file addition happened when the FS was
> still in an unmounted state, the new files weren't written to the
> journal?
>
> Surely in that case the new files would simply not be registered and
> act as free space (as if they had been deleted)?
This is not about a caching service. It is about the way the content of a
mounted disk is made visible to you.
Have you ever wondered how a path name, on your main hard disk, such as
/mnt/usb becomes a link to a USB disk known to the system as /dev/sdd1?
When you type
mount /dev/sdd1 /mnt/usb
It tells the system that, from now on, the directory named "/mnt/usb" becomes
the entry point to the file system that sit at "/dev/sdd1".
Any call such as "ls /mnt/usb" will list the content of the USB disk instead
of the usual content of /mnt/usb.
When the device is unmounted, the directory that serves as its mount point is
restored as a regular directory.
Now, imagine /mnt/usb is not mounted. It is a directory just like any other.
If you copy files to /mnt/usb, they will be copied to that directory and you
have access to them as long as no device is mounted under /mnt/usb.
Then, you mount the USB disk to /mnt/usb. Now, the files are still on the hard
disk (let's say /dev/sda1) but the path /mnt/usb now lists the content of the
USB disk on /dev/sdd1.
It can happen with /boot or /home. Mistakenly copying files to an unmounted
drive copies the files to the underlying file system, in the directory that
usually serves as the mount point for the external file system. Once /boot or
/home is mounted, you don't see the files but they are still taking space on
the disk.
Hope it helps,
Frederic
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