Re: [TCLUG:22757] Raid and other storage stories

[^chewie <chewie@wookimus.net>]

On Tue, Oct 17, 2000 at 05:54:01PM -0500, Carl Wilhelm Soderstrom wrote:
> take a look at the Logical Volume Manager for Linux
> http://linux.msede.com/lvm/
> 
> Heinz Mauelshagen was here in MN, giving a presentation at the U, earlier
> this year. Very interesting stuff; tho I admit most of it flew way over my
> head at the time. :)

I've used, and love, LVM in both the development kernel, 2.4, and the
stable kernel+patches, 2.2.17 + rawio + lvm 0.8final.  It's a
WONDERFUL tool that solves all of my partitioning problems and
desires.  Let's say you have one harddrive, but you'd like to have a
separate parition for a number of mount points in your filesystem:

    ------------------------------
    Desired             Partition
    ------------------------------
    /                   /dev/sda3
    /boot               /dev/sda1
    swap                /dev/sda2
    ------------------------------
    (LVM Partitions     /dev/sda4)
    ------------------------------
    /usr                /dev/vg01/lv_usr
    /home               /dev/vg01/lv_home
    /home/cvs           /dev/vg01/lv_home_cvs
    /home/ftp           /dev/vg01/lv_home_ftp
    /tmp                /dev/vg01/lv_tmp
    /usr/src            /dev/vg01/lv_src
    /usr/local          /dev/vg01/lv_local
    /var                /dev/vg01/lv_var
    /var/cache/cdiso    /dev/vg01/lv_var_cache_cdiso

This may seem like overkill for one drive, but if you think about it,
the directories that contain files that are changing often (relatively
speaking) should be separated from those that are not to combat the
fragmentation that will obviously happen.  /usr/src, /usr/local,
/home, /home/cvs, /var, /tmp are quite dynamic, but /usr, /, and /boot
don't change that often.  Why subject these the /usr to
fragmentation from compiling your kernels in /usr/src, for example.

The other great thing about LVM is that it doesn't matter WHAT
filesystem you use on each Logical Volume parition.  The LV acts as if
it were any other system parition; it is a block device that you have
complete control over.

Also notice that I don't have to worry about logical partitions on the
disk.

Now, if I want to add a new disk and, say, migrate /home/ftp to it, I
can do so simply by paritioning that ENTIRE disk as a physical volume.
I can skip the fdisk step entirely, allowing me to use the otherwise
reserved administration space on the disk.  I can add that physical
volume to volume group vg01 if I desire, or start an entirely new VG.

You don't necessarily have to understand the entire LVM system to use
it in a practical sense, but it is quite powerful and quite flexible.
Just like ReiserFS, LVM *can* be installed on the root parition.

All in all, LVM is a VERY nice complimentary service to any disk
management solution.  RAID, "RAID-less" striping, loop back devices,
etc.  It's all very very cool. ;-)

-- 
  Chad "^chewie, gunnarr" Walstrom <chewie@wookimus.net>
              http://www.wookimus.net/

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