Aug 9, 2011
tom

CentOS Disks and Mounts

Question

I have a web server and I’m confused about how the disk space has been allocated by the company I’m renting it, a dedicated one with a simple RAID mirror at 500Gb. Here is the output of df-h

Filesystem            Size  Used Avail Use% Mounted on
/dev/md1              3.7G  355M  3.4G  10% /
/dev/mapper/vg00-usr  4.0G  1.2G  2.9G  28% /usr
/dev/mapper/vg00-var  4.0G  374M  3.7G  10% /var
/dev/mapper/vg00-home
                      4.0G  4.2M  4.0G   1% /home
none                  2.0G  9.6M  2.0G   1% /tmp
tmpfs                 2.0G     0  2.0G   0% /usr/local/psa/handlers/before-local
tmpfs                 2.0G     0  2.0G   0% /usr/local/psa/handlers/before-queue
tmpfs                 2.0G     0  2.0G   0% /usr/local/psa/handlers/before-remote
tmpfs                 2.0G     0  2.0G   0% /usr/local/psa/handlers/info
tmpfs                 2.0G     0  2.0G   0% /usr/local/psa/handlers/spool

And here is a print from parted

Model: ATA Hitachi HDS5C105 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: msdosNumber  Start   End     Size    Type     File system  Flags
 1      32.3kB  4006MB  4006MB  primary  ext3         raid 
 2      4006MB  6013MB  2007MB  primary  linux-swap        
 3      6013MB  500GB   494GB   primary               raid 

To me it looks like I’m not using much of my available disk space? How would I could about creating a new mount, say 150Gb in the root, something like /data?

Many thanks in advance, and thanks for reading this question.

EDIT

As requested, here is the output of pvdisplay

  --- Physical volume ---
  PV Name               /dev/md3
  VG Name               vg00
  PV Size               460.16 GB / not usable 3.31 MB
  Allocatable           yes 
  PE Size (KByte)       4096
  Total PE              117800
  Free PE               114728
  Allocated PE          3072
  PV UUID               vHgUON-kzqN-TcDt-yhto-fxTW-3nsK-O92Kgx

and here is vgdisplay -v

    Finding all volume groups
    Finding volume group "vg00"
  --- Volume group ---
  VG Name               vg00
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  4
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               460.16 GB
  PE Size               4.00 MB
  Total PE              117800
  Alloc PE / Size       3072 / 12.00 GB
  Free  PE / Size       114728 / 448.16 GB
  VG UUID               4F29RY-NWx6-fzQ3-19tB-pT6Q-G6wg-rHDOkS  --- Logical volume ---
  LV Name                /dev/vg00/usr
  VG Name                vg00
  LV UUID                up8Dud-Zwcd-hmdt-fcLi-3uca-S8gZ-JtpHPt
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                4.00 GB
  Current LE             1024
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0  --- Logical volume ---
  LV Name                /dev/vg00/var
  VG Name                vg00
  LV UUID                Vrjpic-byLm-M7cc-ZTo4-yWoo-zZsL-1DoHpq
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                4.00 GB
  Current LE             1024
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1  --- Logical volume ---
  LV Name                /dev/vg00/home
  VG Name                vg00
  LV UUID                3rJ3o7-M9KU-ml9J-0E8Q-OJEC-ER2F-KwBxVc
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                4.00 GB
  Current LE             1024
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2  --- Physical volumes ---
  PV Name               /dev/md3     
  PV UUID               vHgUON-kzqN-TcDt-yhto-fxTW-3nsK-O92Kgx
  PV Status             allocatable
  Total PE / Free PE    117800 / 114728

Answer

Based on the partition map and df output, I suspect your system is configured in this way:

You have two disks, sda and sdb. Each disk has three partitions, two raid partitions and a swap partition. They’re allocated like so:

  • Your / filesystem lives on a raid mirror occupying partition 1 on both disks.
  • You have two swap partitions, 2 GB each, which are not raided.
  • The third partitions on each disk are connected in a raid mirror 500 GB in size (probably /dev/md0).
  • The raid mirror has been set up in LVM as a single large physical volume (pvdisplay would confirm this).
  • That physical volume has been carved up into at least one volume group (use vgdisplay to see it). It’s likely that there’s only one volume group, named vg00; this is a popular convention.
  • That volume group has at least three logical volumes on it, which are what are mounted on /usr, /var, and /home.

In my guess about how your system is configured, the rest of the space in the physical volume is probably assigned to the single volume group, so to create a new logical volume of 150 GB you’d run lvcreate -n data -L 150G vg00. This would then appear as /dev/vg00-data and be available to be formatted with a filesystem and mounted into /data.

Note: Don’t run that command without making absolutely sure your system really is set up this way. It could cause trouble otherwise.

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