3PAR InForm® OS 2.2.4 Concepts Guide (320-200085 Rev B, March 2009)

2.6

3PAR Storage Concepts and Terminology

3PAR InForm OS Concepts Guide InForm OS Version 2.2.4

Figure 2-3 shows a RAID 50 logical disk with a set size of 3 and a row size of 2 in one row:

Figure 2-3. Data is Striped Across RAID 5 Sets on a RAID 50 Logical Disk

2.1.2.2 Logical Disk Types

The system setup script sets aside Logical Disk (LDs) for logging, for preserved data, and for

Common Provisioning Group (CPG) administration. All other logical disks are available for user

and copy data.

■ Logging LDs are RAID 10 logical disks that can be used to temporarily hold data during disk

failures and disk replacement procedures. Logging logical disks are created by the system

during the initial installation and setup of the storage server. Each controller node in the

system has a 20 GB logging LD.

■ Preserved data LDs are RAID 10 logical disks used to hold preserved data. Preserved data

logical disks are created by the system during the initial installation and setup of the

storage system. The size of the preserved data LD is based on the amount of data cache in

the system.

When disk failures during write operations leave data suspended in cache memory, the

system temporarily preserves this data by writing it to a preserved data logical disk. By

doing so, the system clears the data cache and prevents it from locking up and leading to

wider system failures. When the destination logical disks become available again, the

system automatically writes the preserved data from the preserved data LDs to the

destination logical disks.

■ CPG administration LDs hold the snapshot administration space for all virtual volumes that

draw from the logical disks in a common provisioning group (CPG).

P (E,F)

P (A,B)

P (G,H)

P (C,D)

Step size

Set size*

Row size

RAID 50 logical disk

Chunklet

*Parity set