OpenVZ is nice name-space virtualization, creating chroot jails on steroids, similar in spirit to Solaris zones. It ideal if you want to run single kernel and allocate resources using bean counters as opposed to hard-limits (20% of CPU as opposed to one core). Each slice is called VE.

Disk speed

dpavlin@zut:~$ sudo hdparm -tT /dev/cciss/c1d0 /dev/sda

/dev/cciss/c1d0:
 Timing cached reads:   2184 MB in  2.00 seconds = 1092.39 MB/sec
 Timing buffered disk reads:  324 MB in  3.02 seconds = 107.40 MB/sec

/dev/sda:
 Timing cached reads:   2144 MB in  2.00 seconds = 1071.89 MB/sec
 Timing buffered disk reads:  136 MB in  3.02 seconds =  45.02 MB/sec

Insert joke about enterprise storage

Add disk space to VE

We are using normal Linux LVM with single logical volume for all VEs.

First, resize logical volume:

root@koha-hw:~# vgextend -L +80G /dev/vg/vz
vgextend: invalid option -- L
  Error during parsing of command line.

root@koha-hw:~# lvextend -L +80G /dev/vg/vz
  Extending logical volume vz to 100.00 GB
  Logical volume vz successfully resized

root@koha-hw:~# resize2fs /dev/vg/vz 
resize2fs 1.40-WIP (14-Nov-2006)
Filesystem at /dev/vg/vz is mounted on /vz; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 7
Performing an on-line resize of /dev/vg/vz to 26214400 (4k) blocks.
The filesystem on /dev/vg/vz is now 26214400 blocks long.

root@koha-hw:~# df -h /vz/
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg-vz      99G   20G   79G  21% /vz

Then, take a look how much space does VEs take:

root@koha-hw:~# vzlist -o veid,diskspace,diskspace.s,diskspace.h,diskinodes,diskinodes.s,diskspace.h
      VEID   DQBLOCKS DQBLOCKS.S DQBLOCKS.H   DQINODES DQINODES.S DQBLOCKS.H
    212052   11717220   15728640   20971520      61001     286527   20971520
    212226    6407804   10485760   12582912      69011     435472   12582912

alternativly, you can also execute df inside VEs:

root@koha-hw:~# vzlist -o veid -H | xargs -i sh -c "echo --{}-- ; vzctl exec {} df -h"
--212052--
Filesystem            Size  Used Avail Use% Mounted on
simfs                  15G   12G  3.9G  75% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
tmpfs                 2.0G     0  2.0G   0% /dev/shm
--212226--
Filesystem            Size  Used Avail Use% Mounted on
simfs                  10G  6.2G  3.9G  62% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
tmpfs                 2.0G     0  2.0G   0% /dev/shm

next, we will set diskpace on both VEs (becase we want them to share all available resources) to new logical volume size:

root@koha-hw:~# vzlist -o veid -H | xargs -i vzctl set {} --diskspace 100G:100G --save
Saved parameters for VE 212052
Saved parameters for VE 212226

This VEs are not in production, and one is development version of another. When we move to production, we want to enforce more strict limit on disk usage, to protect production machine from running out of disk space in case the development one goes wild.