compression on external hard drive?

compression on external hard drive?

[Xavier Gnata]

Hello list,

Nowdays, external hard drives are mounted automagically by kde, gnome or 
whatever else.
How is it suppose to work with external hard drives using btrfs with 
compression?
If a btrfs filesystem lzo-compressed is mounted without the 
|compress=|xxx option then all the newly created files are uncompressed, 
aren't then?
Would it be possible to detect if a file system is compressed  and to 
mount it *automatically* and accordingly (except otherwise explicitly 
stated by the user) with/without the lzo/gzip option?

Xavier

Re: compression on external hard drive?

[Duncan]

Xavier Gnata posted on Sun, 26 May 2013 00:11:55 +0200 as excerpted:

> Nowdays, external hard drives are mounted automagically by kde, gnome or
> whatever else.
> How is it suppose to work with external hard drives using btrfs with
> compression?
> If a btrfs filesystem lzo-compressed is mounted without the
> |compress=|xxx option then all the newly created files are uncompressed,
> aren't then?
> Would it be possible to detect if a file system is compressed  and to
> mount it *automatically* and accordingly (except otherwise explicitly
> stated by the user) with/without the lzo/gzip option?

There's a proposal to do something like ext3/4's default options as set 
by tune2fs, at some point, presumably before btrfs loses the "unstable 
disk format" and under heavy development warnings.  However, there's 
nothing like that yet, AFAIK, so most options must be set per-mount.

There's a lot you can do with udev events, however, and strongly suspect 
either compression-detection, or match-against-a-list-and-compress (or 
don't compress if the default is compression otherwise) if the UUID/LABEL 
is listed.

Alternatively, at least kde can be set not to automount specific UUIDs/
LABELs, and then there's always the traditional fstab option, and I think 
either fstab entered drives are ignored by the automount system or 
they're automounted with options from fstab (I have that kde subsystem 
entirely disabled here so it doesn't automount anything, so I'm not sure 
which it actually does).

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

Re: compression on external hard drive?

[xavier.gnata]

On 05/26/2013 04:23 AM, Duncan wrote:
> Xavier Gnata posted on Sun, 26 May 2013 00:11:55 +0200 as excerpted:
>
>> Nowdays, external hard drives are mounted automagically by kde, gnome or
>> whatever else.
>> How is it suppose to work with external hard drives using btrfs with
>> compression?
>> If a btrfs filesystem lzo-compressed is mounted without the
>> |compress=|xxx option then all the newly created files are uncompressed,
>> aren't then?
>> Would it be possible to detect if a file system is compressed  and to
>> mount it *automatically* and accordingly (except otherwise explicitly
>> stated by the user) with/without the lzo/gzip option?
> There's a proposal to do something like ext3/4's default options as set
> by tune2fs, at some point, presumably before btrfs loses the "unstable
> disk format" and under heavy development warnings.  However, there's
> nothing like that yet, AFAIK, so most options must be set per-mount.
>
> There's a lot you can do with udev events, however, and strongly suspect
> either compression-detection, or match-against-a-list-and-compress (or
> don't compress if the default is compression otherwise) if the UUID/LABEL
> is listed.
>
> Alternatively, at least kde can be set not to automount specific UUIDs/
> LABELs, and then there's always the traditional fstab option, and I think
> either fstab entered drives are ignored by the automount system or
> they're automounted with options from fstab (I have that kde subsystem
> entirely disabled here so it doesn't automount anything, so I'm not sure
> which it actually does).
>
Ok I'm going to play with udev event and have a lot at what kde4.10.3 
can do.
However, I hope this will be solved at fs level once the dust has settled.

Xavier