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Old 10-17-2012, 06:28 PM   #1
Registered: Apr 2010
Distribution: FC17
Posts: 132

Rep: Reputation: 1
Need advise after adding 4TB disk (FC17, KDE)


My FC17+KDE system resides on a pair of 130GB SAS disks
arranged in RAID 0 array /dev/sda and using LVM:

<root localhost.localdomain>.../root>df
Filesystem                   1K-blocks     Used Available Use% Mounted on
rootfs                       102534472 12835448  84490552  14% /
devtmpfs                       8173528        0   8173528   0% /dev
tmpfs                          8218184      156   8218028   1% /dev/shm
tmpfs                          8218184     1320   8216864   1% /run
/dev/mapper/VolGroup-lv_root 102534472 12835448  84490552  14% /
tmpfs                          8218184        0   8218184   0% /sys/fs/cgroup
tmpfs                          8218184        0   8218184   0% /media
/dev/sda1                      1032088   123232    856428  13% /boot
/dev/mapper/VolGroup-lv_home 135079152 74010164  54207372  58% /home
Recently, after seeing the disk usage growing fast,
I bought a pair of 2TB SAS disks, arranged them too
in another RAID 0 array (well, it had been actually reported
as 3.8TB, the usual disk manufacturers tricks of redefining
measurment units) and started looking for a way to create
an lvm2 volume on the new disk and to mount it on /home/GRAPHICS
(the largest disk space consuming directory).

During the system installation I liked the "disk druid" GUI
program but after some reading I saw it can't be used after the
installation (at least, not in a simple way).

I installed "sys-config-lvm" and "gparted" and looked also
at "lvm" and "cfdisk" and "fdisk".
I would prefate a nice GUI app like "disk druid" but I couldn't
find (or missed) an app to do what I need.
At first I created an "ext4" partition on the /dev/sdb but
then I remembered that I should create physical volume instead
so I deleted the partition.
The "system-config-lvm" didn't see the /dev/sdb disk at all,
in "gparted", looking at the avaliable types of creating a partition
I didn't see any option to create a physical volume (which, AFAIK
is needed to create logical volumes group and then lvm2 volume),
starting "cfdisk" resulted in the following message:

Warning!!  Unsupported GPT (GUID Partition Table) detected. Use GNU Parted.
and then presented what looks like 2TB+1.8TG partitions:

                                            cfdisk (util-linux 2.21.2)

                                               Disk Drive: /dev/sdb
                                       Size: 3994319585280 bytes, 3994.3 GB
                              Heads: 255   Sectors per Track: 63   Cylinders: 485615

     Name             Flags           Part Type       FS Type                [Label]              Size (MB)
     sdb1             NC               Primary        GPT                                        2199023.26      *
                                       Pri/Log        Free Space                                 1795296.33      *

I've read about LINUX partition size limits and learned that
I have one more obstacle of which I didn't think earlier.

lookin at /dev/sdb with "gparted" it shows the entire disk "unallocated".

I'm beginning to feel "lost" in what initially looked like a sinple
task of adding a disk to the system.

Can anyone guide me as to what actions should I take to create
ext4 filesystem on LV of 3.8TB on PV resiging on /dev/sdb ?

Old 10-19-2012, 03:50 AM   #2
Registered: Oct 2006
Location: Seattle, Washington
Distribution: Gentoo, LinuxMint, Arch Linux
Posts: 99

Rep: Reputation: 18
GParted is a really nice GUI but it doesn't support LVM. I know Red Hat / Fedora has a GUI tool specifically for LVM. But I don't know of a GUI that does both LVM and File System stuff.

I don't have much experience with software RAID. But assuming /dev/sdb is a RAID block device I would do the following things.
(But first... Note: Making changes to partition tables and filesystems can result in complete loss of data. You are ultimately responsible for your data. IE, have a backup, understand commands, don't copy/paste commands.)

Use fdisk to delete all partitions

pvcreate /dev/sdb
vgextend VolGroup /dev/sdb
lvcreate -l 100%PVS -n lv_graphics VolGroup /dev/sdb
File system and mount:
mkfs.ext4 /dev/mapper/VolGroup-lv_graphics
mount /dev/mapper/VolGroup-lv_graphics /home/GRAPHICS
Size restrictions shouldn't be an issue here. EXT4 supports up to 16TB and I honestly don't know if there is any limit to LVM.
I would caution you about the RAID 0. Make sure you have backups.

Another thing you can do is just attach both disks and use LVM to combine them into a single volume. That might be easier to manage then a RAID. You could more easily expand or shrink the volume.

Hope that helps some.
Old 10-20-2012, 07:37 AM   #3
Registered: Apr 2010
Distribution: FC17
Posts: 132

Original Poster
Rep: Reputation: 1
Hi jasohl, thanks for the reply.

In fact, after some more reading and searching among the commands
I found that using the "gdisk /dev/sdb" I can create the GPT-type
partition ("LINUX LVM", type code: "8E00") and after that
I could use the "system-config-lvm" to create the physical
volume, logical group and logical volume. Currently, it's
mounted on a slightly differently named directory than my
final intention:

Filesystem                                 1K-blocks     Used  Available Use% Mounted on
rootfs                                     102534472 12850732   84475268  14% /
devtmpfs                                     8173528        0    8173528   0% /dev
tmpfs                                        8218184      152    8218032   1% /dev/shm
tmpfs                                        8218184     1256    8216928   1% /run
/dev/mapper/VolGroup-lv_root               102534472 12850732   84475268  14% /
tmpfs                                        8218184        0    8218184   0% /sys/fs/cgroup
tmpfs                                        8218184        0    8218184   0% /media
/dev/sda1                                    1032088   123232     856428  13% /boot
/dev/mapper/VolGroup-lv_home               135079152 73994472   54223064  58% /home
/dev/mapper/VolGroup_graphics-lv_graphics 3839491472 23288632 3621167912   1% /home/user/GRAPHICS_lv
After I'll compare the contents of the old GRAPHICS
and the new GRAPHICS_lv directories, I'll need to
boot LINUX into command line mode (without the desktop coming up),
to rename "GRAPHICS" to "GRAPHICS_old", to rename "GRAPHICS_lv"
to "GRAPHICS", to edit appropriately the /etc/fstab, to reboot
and hopefully the GUI (with various links from GRAPHICS to the desktop)
won't notice any change.

Now I need to find out how to pause the boot process and
force the command line boot...

Old 10-22-2012, 02:33 AM   #4
Registered: Apr 2010
Distribution: FC17
Posts: 132

Original Poster
Rep: Reputation: 1

It took some time to figure out where to add the "3" on the grub2 menu (most searches showed a single line command,
not a multi-line entry) but finally I could boot without desktop starting, to rename "GRAPHICS" to "GRAPHICS_old",
to attempt renaming "GRAPHICS_lv" to "GRAPHICS, to encounter an error "device busy" (or something like
thhis), to attempt unmount, to get the same error, to rename back, to reboot normally, to comment the line in /etc/fstab
which mounts the new disk, to reboot into command line, this time to successfully rename everything
as I want, to replace /etc/fstab with the one with mount command to "GRAPHICS" instead of "GRAPHICS_lv"
and after reboot - everything is as I want it: new 3.6 TB disk (hardware RAID 0) is mounted on "GRAPHICS"

Thanks for all the help,


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