Storage System

Physical Volume: Name for an actual disk e.g SSA, SCSI disk; a PV can belong to a VG only

Volume Group: It is the largest unit of storage allocation; It contains multiple PV under a single VG name. The combined storage of all the PV makes a total space of VG which is used in turn by File Systems and Logical Volumes. A VG is splitted into PP; the size of PP within VG remains constant.

Why to create separate VG? e.g datavg and rootvg.
ans: To separate userdata from OS files; Disaster Recovery; Data portability; Data integrity and security | Maintenance is easy because you can update or reinstall OS without restoring data.
You can make VG unavailable using VARRYOFFVG.
There can be 255 VGs per System.

Physical Partition: PP is the division of PV. It is the basic unit of disk space allocation.
Default max no. of PP per PV is 1016. PP size cannot be changes dynamically but the number of PP per PV can be changed dynamically in mulitples of 1016. (i.e 1016, 2032, ...)

(Note: If you increase the more than 1016 PP per PV, then no. of PV per VG will be reduced)

Logical Volume: LV contains one or more LP within the VG. LV may span the PV if the multiple PV within the VG. LV size may be increased dynamically using SMIT even when users are working on that LV. However, the size cannot be reduced easily.

MAX PV=32 (128 BIG VG)
MAX LV=255 (512 BIG VG)
MAX VG =255 per system

Logical Partition: LP within a VG is the same size as PP


LVM does mapping between LV (logical view of storage) and PV (actual view of storage).

Why LVM?

In traditional Storage System, there were many limitation:

1. Requirement of Contiguous Disk Space
2. Max partition size=Max Disk size (i.e Partition size cannot span multiple disks)
Thus no file system can be larger than Disk size
3. Pre-plan the partition size requirement, as after creation of partition, the partition cannot be resized.

To tackle with these problems, LVM (Logical Volume Manager) was developed.

Benefits of LVM:

1. LV solves the non-contiguous disk space requirement
2. LV can span to mulitiple disks
3. Dynamically increase LV size
4. LV can be mirrored
5. Harddisk easily added to the system.
6. LV can be relocated.

SAN storage

SAN (Storage Area Network):

Why SAN?

How many drives your standalone PC can have?
ans: 2-3

Is that enough for the organization?
ans: of course not

If you lose your drive, what happens?
ans: total disaster, u lose all your data

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ok then, SAN has all the solution...
Make Storage section consisting huge array of drives and allocate LUNs (Logical Unit Number) to the clients as per they demand.
Like One of my client need 2 GB for rootvg of AIX server. Then I allocate 1 LUN of 2 GB and give to the client.

Following is the connection configuration in SAN:

[100s of clients]-----HIGH SPEED FIBRE CHANNEL----[Tera byte storage]

Clients get access to their LUN via Fibre Channel and thus can be said that they are physically connected.

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For Redundancy RAID is implemented

RAID 0 --- striping (for high performance)
RAID 1 --- mirroring (for safe side operation i.e even a single drive fails, u still have another as backup)
RAID 5 --- parity bit enabled (data recovery even if one disk failed)

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What about NAS?
NAS is similar thing, but it uses Ethernet instead of Fibre Channel. So NAS is slower than SAN.

Following is the connection configurtion in NAS

[CLIENTS]------ETHERNET---------[SERVER]------------[STORAGE]

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