Best practice is to have a good design on system disk during deployment, as after the install it can be very difficult to review the OS storage.

Logical Volume Manager brings a virtualization level on disks and partitions management, with more flexibility, resizing, moving…

Why using multiple disks on a production server ?

• All access to data doesn't need the same level of availability, as cost is important, you can for example assign slow disks on archiving datas, high speed for database…
• For backup, to be able to use different backup policies we have to split the datas on different disks. On VMware the increment for backup is the disk, so to make a consistent backup, you have to split maybe the database on one disk, the OS on another, archives on another…
• On physical servers, we can also do snapshots on SAN disks, so it's important to think you storage
• On virtual servers, backup increment is the disk (Ex VMware), so be aware of you disk configuration
• LVM on Linux and AIX is also a best practice. LVM will bring flexibility in volume resizing, disks movements…

Why using LVM ?

* A volume manager is required (based installed) on AIX. On AIX, all disks are assigned to a volume group to be used (except special 
case with Oracle RAC...). OS disk is also assign to a volume group, no boot partition, but instead a boot logical partition into the 
rootvg volume group
* On Linux you can work on different ways, using static partitions, which can be very complicated to resize, with server downtime. 
So better usage can be done if you use a volume manager (LVM). One filesystem has to be created based on a partition: /boot. All 
other filesystems (volumes) can be included into a Volume group, including the the swap volume.

List Linux physical disks and partitions

[root@redhat01 ~]# lsscsi -s
[0:0:0:0]    disk    VMware   Virtual disk     2.0   /dev/sda    268GB
[0:0:0:1]    disk    VMware   Virtual disk     2.0   /dev/sdb    268GB

[root@redhat01 ~]# fdisk -l

Disk /dev/sda: 268.4 GB, 268435456000 bytes, 524288000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0009f12e

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000   83  Linux
/dev/sda2         1026048   524287999   261630976   8e  Linux LVM

List AIX physical disks, no partitions on AIX

[root@aix01]/export/softs/openssl# lsdev -Cc disk
hdisk0  Available C5-T1-01 MPIO IBM 2076 FC Disk
hdisk1  Available C5-T1-01 MPIO IBM 2076 FC Disk
hdisk2  Available C5-T1-01 MPIO IBM 2076 FC Disk
hdisk3  Available C5-T1-01 MPIO IBM 2076 FC Disk
hdisk4  Available C5-T1-01 MPIO IBM 2076 FC Disk
hdisk5  Available C8-T1-01 MPIO Other FC SCSI Disk Drive
hdisk6  Available C5-T1-01 MPIO Other FC SCSI Disk Drive

It a disk on AIX or Linux, or a disk partition on Linux, which has a type LVM, with a LVM physical volume identifier PVID or PV UUID (uniq ID)

Example a partition on Linux

[root@redhat01 ~]# pvs
  PV         VG     Fmt  Attr PSize    PFree
  /dev/sda2  centos lvm2 a--  <249.51g    0

[root@LIN-SDSMON01-VH ~]# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sda2
  VG Name               centos
  PV Size               <249.51 GiB / not usable 2.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              63874
  Free PE               0
  Allocated PE          63874
  PV UUID               jipWn3-SXwO-GS8R-fcj0-xxxx-xxxx-hd2Mx3

Example a disk on AIX

[root@aix01]/root# lspv
hdisk10         00c2fcc8dfe7288e                    altinst_rootvg
hdisk0          00fa343b8f050a76                    rootvg          active
hdisk5          00fa343b99011146                    None
hdisk6          00fa343b990e37a0                    None
hdisk1          00fa343b8f050ea7                    None
hdisk2          00fa343b8f01b1e2                    rootvg          active
hdisk7          00fa343b990e38be                    None
hdisk8          00fa343b990e39ea                    nimvg           active
hdisk9          00fa343b990e3b0b                    nimvg           active
hdisk11         00c2fcc8dfe729fd                    altinst_rootvg
hdisk3          00fa343b98f0c47d                    SOURCEvg
hdisk4          00fa343b98f0c47d                    SOURCEvg

[root@aix01]/root# lspv hdisk0
PHYSICAL VOLUME:    hdisk0                   VOLUME GROUP:     rootvg
PV IDENTIFIER:      00fa34xxxxx50a76 VG IDENTIFIER     00c2fcc800004c0000000xxxxxxd3dce
PV STATE:           active
STALE PARTITIONS:   0                        ALLOCATABLE:      yes
PP SIZE:            128 megabyte(s)          LOGICAL VOLUMES:  21
TOTAL PPs:          639 (81792 megabytes)    VG DESCRIPTORS:   1
FREE PPs:           112 (14336 megabytes)    HOT SPARE:        no
USED PPs:           527 (67456 megabytes)    MAX REQUEST:      512 kilobytes
FREE DISTRIBUTION:  01..00..00..00..111
USED DISTRIBUTION:  127..128..127..128..17
MIRROR POOL:        None

A volume group 'll agregate one or multiple physical disks. In a VG, the space is devide in extend with a fix size, this size can't be changed. It a increment when you create logical volumes. In a VG, you can add or remove PVs.

A system can manage multiple VG, and each VG can have up to 1024 PV on AIX, and no limit on Linux

Example a VG on Linux

[root@redhat01 ~]# vgs
  VG     #PV #LV #SN Attr   VSize    VFree
  centos   1   2   0 wz--n- <249.51g    0

[root@redhat01 ~]# vgdisplay
  --- Volume group ---
  VG Name               centos
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  17
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <249.51 GiB
  PE Size               4.00 MiB
  Total PE              63874
  Alloc PE / Size       63874 / <249.51 GiB
  Free  PE / Size       0 / 0
  VG UUID               9fkgje-aAf5-Zb8m-YPBi-khAj-xxxx-RoOqCZ

Example a VG on AIX

[root@aix01]/root# lsvg rootvg
VOLUME GROUP:       rootvg                   VG IDENTIFIER:  00c2fcc800004c00000001xxxx1d3dce
VG STATE:           active                   PP SIZE:        128 megabyte(s)
VG PERMISSION:      read/write               TOTAL PPs:      1278 (163584 megabytes)
MAX LVs:            256                      FREE PPs:       224 (28672 megabytes)
LVs:                21                       USED PPs:       1054 (134912 megabytes)
OPEN LVs:           20                       QUORUM:         1 (Disabled)
TOTAL PVs:          2                        VG DESCRIPTORS: 3
STALE PVs:          0                        STALE PPs:      0
ACTIVE PVs:         2                        AUTO ON:        no
MAX PPs per VG:     32512
MAX PPs per PV:     1016                     MAX PVs:        32
LTG size (Dynamic): 512 kilobyte(s)          AUTO SYNC:      no
HOT SPARE:          no                       BB POLICY:      relocatable
PV RESTRICTION:     none                     INFINITE RETRY: no
DISK BLOCK SIZE:    512                      CRITICAL VG:    no
FS SYNC OPTION:     no                       CRITICAL PVs:   no
ENCRYPTION:         no

[root@aix01]/root# lsvg -p rootvg
rootvg:
PV_NAME           PV STATE          TOTAL PPs   FREE PPs    FREE DISTRIBUTION
hdisk2            active            639         112         01..00..00..00..111
hdisk0            active            639         112         01..00..00..00..111

A volume group can be partitionned logicaly by defining Logical Volumes. These logical volumes can be extended, sometimes reduced, move from on PV to another into the same VG (useful for migration to new disks).

On Linux

[root@redhat01 ~]# lvs
  LV   VG     Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root centos -wi-ao---- <247.51g
  swap centos -wi-ao----    2.00g
[root@redhat01 ~]# lvdisplay
  --- Logical volume ---
  LV Path                /dev/centos/swap
  LV Name                swap
  VG Name                centos
  LV UUID                Jd4pYt-5OSL-Ks0c-ywGe-yJCu-xxxx-DSyaFs
  LV Write Access        read/write
  LV Creation host, time localhost, 2015-09-23 16:24:57 +0200
  LV Status              available
  # open                 2
  LV Size                2.00 GiB
  Current LE             512
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

  --- Logical volume ---
  LV Path                /dev/centos/root
  LV Name                root
  VG Name                centos
  LV UUID                WQLbI3-M3sb-TtF6-enML-xxxx-pb3C-MqVVD0
  LV Write Access        read/write
  LV Creation host, time localhost, 2015-09-23 16:24:57 +0200
  LV Status              available
  # open                 1
  LV Size                <247.51 GiB
  Current LE             63362
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

On AIX, list LV per VG

[root@aix01]/export/softs/openssl# lsvg | xargs lsvg -l
rootvg:
LV NAME             TYPE       LPs     PPs     PVs  LV STATE      MOUNT POINT
hd5                 boot       1       2       2    closed/syncd  N/A
hd6                 paging     33      66      2    open/syncd    N/A
hd8                 jfs2log    1       2       2    open/syncd    N/A
hd4                 jfs2       92      184     2    open/syncd    /
hd2                 jfs2       91      182     2    open/syncd    /usr
hd9var              jfs2       48      96      2    open/syncd    /var
hd3                 jfs2       208     416     2    open/syncd    /tmp
hd1                 jfs2       197     394     2    open/syncd    /home
hd10opt             jfs2       48      96      2    open/syncd    /opt
hd11admin           jfs2       2       4       2    open/syncd    /admin
lg_dumplv           sysdump    18      18      1    open/syncd    N/A
livedump            jfs2       4       8       2    open/syncd    /var/adm/ras/livedump
roothomelv          jfs2       88      176     2    open/syncd    /root
corelv              jfs2       16      32      2    open/syncd    /var/core
fslv01              jfs2       8       16      2    open/syncd    /tftpboot
lg_dumplv2          sysdump    18      18      1    open/syncd    N/A
nimvg:
LV NAME             TYPE       LPs     PPs     PVs  LV STATE      MOUNT POINT
loglv00             jfs2log    1       1       1    open/syncd    N/A
mksysblv            jfs2       6160    6160    5    open/syncd    /export/mksysb
aix71lv             jfs2       1680    1680    3    open/syncd    /export/aix71
powerlinuxlv        jfs2       80      80      1    closed/syncd  /export/powerlinux
softlv              jfs2       2761    2761    4    open/syncd    /export/softs

A Logical Volume 'll have a mount point accessible in the unix tree, called a filesystem.