HP 3PAR StoreServ 7450 4-node HP 3PAR StoreServ Storage Concepts Guide (OS 3.1 - Page 34

Logical Disks, Overview, Logical Disks and Common Provisioning Groups, Logical Disk Types

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7 Logical Disks Overview A Logical Disk (LD) is a collection of physical disk chunklets arranged as rows of RAID sets. Each RAID set is made up of chunklets from different physical disks. Logical disks are pooled together in Common Provisioning Groups (CPGs) which allocate space to virtual volumes. Creating CPGs maps out the data layout parameters for the creating logical disks. Logical disks are created automatically by the system when virtual volumes are created from CPGs. The RAID type, space allocation, growth increments and other logical disk parameters can be set when you create a CPG or modified after creating a CPG. For information about CPGs, see "Common Provisioning Groups" (page 39). Logical Disks and Common Provisioning Groups Creating a Common Provisioning Group (CPG) establishes a virtual pool of logical disks that can grow on demand. When you create virtual volumes, the system creates all underlying logical disks for you automatically. Volumes associated with a CPG draw logical disk space from the virtual pool as needed, allocating space on demand. As the volumes that draw from a CPG require additional storage, the system automatically creates additional logical disks and adds them to the pool. Once you create a CPG, you can add and remove logical disks. You can also specify advanced logical disk parameters when creating CPGs. This allows you to exercise a greater degree of control over how the system creates logical disks within the CPG. NOTE: Creating virtual copies or snapshots requires the HP 3PAR Virtual Copy Software license. For more information, see "HP 3PAR Software" (page 9) Logical Disk Types The following logical disk types provide storage space to virtual volumes: • User logical disks provide user storage space to virtual volumes. The user space contains the user data and is exported as a LUN to the host. • Snapshot data logical disks provide the storage space for snapshots or virtual copies. The snapshot space contains copies of user data that changed since the previous snapshot of the volume was created. • Snapshot administration logical disks provide the storage space for snapshot administration. The administration space is used to track changes to the volume since the previous snapshot was created. The system sets aside logical disks for logging, for preserved data, and for system administration. These logical disks are multi-level logical disks with three way mirrors for enhanced redundancy and performance. The following logical disk types are created by the system: • logging logical disks are RAID 10 logical disks that are 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 system. Each controller node in the system has a 60 GB logging LD. • preserved data logical disks 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 multiple 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 34 Logical Disks

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7 Logical Disks
Overview
A Logical Disk (LD) is a collection of physical disk chunklets arranged as rows of RAID sets. Each
RAID set is made up of chunklets from different physical disks. Logical disks are pooled together
in Common Provisioning Groups (CPGs) which allocate space to virtual volumes. Creating CPGs
maps out the data layout parameters for the creating logical disks. Logical disks are created
automatically by the system when virtual volumes are created from CPGs. The RAID type, space
allocation, growth increments and other logical disk parameters can be set when you create a
CPG or modified after creating a CPG. For information about CPGs, see
“Common Provisioning
Groups” (page 39)
.
Logical Disks and Common Provisioning Groups
Creating a Common Provisioning Group (CPG) establishes a virtual pool of logical disks that can
grow on demand. When you create virtual volumes, the system creates all underlying logical disks
for you automatically. Volumes associated with a CPG draw logical disk space from the virtual
pool as needed, allocating space on demand. As the volumes that draw from a CPG require
additional storage, the system automatically creates additional logical disks and adds them to the
pool. Once you create a CPG, you can add and remove logical disks. You can also specify
advanced logical disk parameters when creating CPGs. This allows you to exercise a greater
degree of control over how the system creates logical disks within the CPG.
NOTE:
Creating virtual copies or
snapshots
requires the HP 3PAR Virtual Copy Software license.
For more information, see
“HP 3PAR Software” (page 9)
Logical Disk Types
The following logical disk types provide storage space to virtual volumes:
•
User
logical disks provide user storage space to virtual volumes. The user space contains the
user data and is exported as a LUN to the host.
•
Snapshot data
logical disks provide the storage space for snapshots or virtual copies. The
snapshot space contains copies of user data that changed since the previous snapshot of the
volume was created.
•
Snapshot administration
logical disks provide the storage space for snapshot administration.
The administration space is used to track changes to the volume since the previous snapshot
was created.
The system sets aside logical disks for logging, for preserved data, and for system administration.
These logical disks are multi-level logical disks with three way mirrors for enhanced redundancy
and performance. The following logical disk types are created by the system:
•
logging
logical disks are RAID 10 logical disks that are 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 system. Each controller node in the system has
a 60 GB logging LD.
•
preserved data
logical disks 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 multiple 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
34
Logical Disks