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Limitations
This section discusses limitations in the following areas:
- Volume groups
- Physical volumes in volume groups
- Physical partitions per volume group
- Logical volumes per volume group
- Logical partitions per logical volume
- Mirrored copies of a logical volume
Volume Groups
The limit of 256 possible volume groups has been a part of AIX since
LVM's inception in AIX 3.1. With the advent of a 64-bit
operating system, the volume group limit rises to 4,096 entities.
Because of constant increases in disk capacity and the use of multiple
physical and logical volumes within the volume group, the number of
volume groups is not a hindrance to customers.
|
Parameter
| LVM
| VxVM
|
| Equivalent
| Volume Groups
| Disk Groups
|
| Limits
| 32-bit: 256
64-bit: 4,096
| None
|
Physical Volumes in Volume Groups
From AIX 3.1 to AIX 4.2, the limit of 32 disks per volume
group was fixed with a "standard" volume group. Starting with AIX
4.3, the user can create a "big" volume group that has the
expanded disk count. Volumes created at an older level of AIX are
upwardly compatible; that is, a volume group created on AIX 3.1 or
3.2 can be introduced into a system running on AIX 4.3.
However, downward compatibility of volume groups is not
supported. Again, because of the rapid growth of commercial disk
volumes and the ability to specify physical partition sizes within a volume
group, the current limit of 128 disks per volume group is not a
problem.
| Parameter
| LVM
| VxVM
|
| Equivalent
| Physical Volumes in Volume Group
| Disk Access & Disk Media
|
| Limits
| Standard: 32
or
Big: 128
| None
|
Physical Partitions per Volume Group
The following table reviews the limitations in the physical partitions per
volume group.
| Parameter |
LVM
| VxVM
|
| Equivalent
| Physical Partitions
| Subdisks
|
| Limits
| 1,016 per disk
or
1016*128 = 130,048 per volume group
| |
Logical Volumes per Volume Group
The following table reviews the limitations in the logical volumes per
volume group.
| Parameter
| LVM
| VxVM
|
| Equivalent
| Logical Volumes
| Volume
|
| Limits
| Standard: 256
or
Big: 512
| None
|
Logical Partitions per Logical Volume
The following table reviews the limitations in the logical partitions per
logical volume.
| Parameter
| LVM
| VxVM
|
| Equivalent
| Logical Partitions in a Logical Volume
| Subdisks per plex
|
| Limits
| 32,512
| 4,096
|
Mirrored Copies of a Logical Volume
At the present time, the capability to have more than three mirrors is not
seen as a necessity. Along with the increased disk requirement, the
more copies a logical has, the longer "writes" will take because all
"writes" must return from their respective disk platters before a
"write" returns to the file system. Experience shows that
customers tend to use only two of the three possible mirrored copies.
| Parameter
| LVM
| VxVM
|
| Equivalent
| Mirrors per Logical Partition
| Copies per plex
|
| Limits
| 3
| 32
|
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