Re: [gentoo-user] LVM for data drives but not the OS

[Alan McKinnon]

Apparently, though unproven, at 23:01 on Friday 08 April 2011, Dale did opine 
thusly:

> Dale wrote:
> > root@fireball / # pvcreate /dev/sdb
> >
> >   Physical volume "/dev/sdb" successfully created
> >
> > root@fireball / #
> >
> > Step one done.  It didn't puke on my keyboard.  lol
> >
> > Now to see what else I can get into.  Not going to put anything
> > important on it tho.  Just a temporary thing right now.  Just getting
> > my feet wet.
> >
> > Dale
> >
> > :-)  :-)
>
> More progress.
>
> root@fireball / # ls -al /dev/mapper/
> total 0
> drwxr-xr-x  2 root root      80 Apr  8 15:56 .
> drwxr-xr-x 16 root root    4400 Apr  8 15:56 ..
> crw-rw----  1 root root 10, 236 Apr  8 04:39 control
> lrwxrwxrwx  1 root root       7 Apr  8 15:56 sdb--vg-test -> ../dm-0
> root@fireball / # pvdisplay
>    --- Physical volume ---
>    PV Name               /dev/sdb
>    VG Name               sdb-vg
>    PV Size               232.83 GiB / not usable 2.58 MiB
>    Allocatable           yes
>    PE Size               4.00 MiB
>    Total PE              59604
>    Free PE               46804
>    Allocated PE          12800
>    PV UUID               kopUKm-lXy1-7tiq-FuQ2-Xhs5-tGqN-Ls4R1v
>
> root@fireball / # vgdisplay
>    --- Volume group ---
>    VG Name               sdb-vg
>    System ID
>    Format                lvm2
>    Metadata Areas        1
>    Metadata Sequence No  2
>    VG Access             read/write
>    VG Status             resizable
>    MAX LV                0
>    Cur LV                1
>    Open LV               0
>    Max PV                0
>    Cur PV                1
>    Act PV                1
>    VG Size               232.83 GiB
>    PE Size               4.00 MiB
>    Total PE              59604
>    Alloc PE / Size       12800 / 50.00 GiB
>    Free  PE / Size       46804 / 182.83 GiB
>    VG UUID               5OSiWZ-rWza-uKJ2-rVMO-f38G-NBHx-dmAE1K
>
> root@fireball / # lvdisplay
>    --- Logical volume ---
>    LV Name                /dev/sdb-vg/test
>    VG Name                sdb-vg
>    LV UUID                mixhOb-La6D-BwG4-Uz3l-P0ci-oGg5-YI3mN8
>    LV Write Access        read/write
>    LV Status              available
>    # open                 0
>    LV Size                50.00 GiB
>    Current LE             12800
>    Segments               1
>    Allocation             inherit
>    Read ahead sectors     auto
>    - currently set to     256
>    Block device           254:0
>
> root@fireball / #
>
> I'm still trying to figure out how the naming part works tho.  Now to
> mount it and put something on it.  See if it works.

Naming can vary a lot depending on udev rules. There will be one canonical 
name and one or more other things that symlink to it.

Likely the canonical stuff will be /dev/mapper/.....
and the symlinks will be in /dev/sdb-vg/.....
cd and ls will see you right :-)


 
> Let me know if something doesn't look right.  Otherwise, I'll keep
> playing around with it.

Cool. So now you have a 250G PV, and it's the the only PV in it's volume 
group. You've made a 50G LV called "test"

Cool so far. Now make a few more LVs (check the man pages, I'm doing this from 
memory):

lvcreate -L 20G -n test2 sdb-vg
lvcreate -L 30G -n test3 sdb-vg

mkfs them:
mkfs.<your_choice> /dev/sdb-vg/test{,2,3}

mount points:
mkdir /mnt/test{,2,3}

mount them:
mount /dev/sdb-vg/test /mnt/test

Whoop-dee-doo. Now you can copy stuff there and do whatever you do with 
filesystems. Let's assume you have music on the first one "test". Let's also 
assume you get more music and it's more than 50G; say you need another 20. 
Easy-peasy, grow the filesystem, grow the LV:

lvextend -L +20G /dev/sdb-vg/test
resize2fs /dev/sdb-vg/test

That's it. Nothing more. Without LVM, you'd be off down to the 'puter store 
looking to buy 70 CDs to do that :-)

It's important to remember that once you've made /dev/sdb into a PV, you will 
never touch that device again. You will especially never fdisk or mkfs it - 
all that is done on the block device that LVM gives you - /dev/sdb-vg/test



-- 
alan dot mckinnon at gmail dot com