[clug-talk] LVM reduction

[Richard Carter]

William,

Thanks for you informative reply.  I'll take that into account.

Robin

On Dec 13, 2007 12:20 AM, William Astle <lost at l-w.ca> wrote:

> Richard Carter wrote:
> > Hi Folks,
> >
> > My Debian box has a 160GB HD configured as one volume group containing
> > six logical volumes one of which is home of size 138GB.  I want to use
> > lvreduce to shrink home so that I have space to increase the size of my
> > other logical volumes: eg. usr and root.   The manual page for lvreduce
> > says, in part, "You  should  therefore  ensure  that  any  filesystem
> > on the volume is resized before running lvreduce so that the  extents
> > that  are  to  be removed are not in use."  However, only 8GB, out of
> > 138GB in home are in use so this seems to me to be unecessary. Is this
> > correct?
>
> Not correct actually. The file system itself uses the entire size of the
> partition/volume even if it is essentially empty. You have to resize the
> file system so that it knows that it doesn't have that space any more
> and to make sure it doesn't have any data stored in the area that is
> being removed. Remember, you don't know where the data is stored in the
> partition, either.
>
> Put another way, the file system itself is laid out based on the size of
> the volume and it knows how big the volume is. If you don't resize it
> before shrinking the volume, you will damage the file system and there
> is an extremely high chance of data loss.
>
> --
> William Astle
> finger lost at l-w.ca for further information
>
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