HP P6000 Continuous Access Software - Manual (Page 269)

◦ Must be in a normal operational state. See resources Operational states .
◦ Must use mirrored cache. See virtual disks Cache policies .
◦ Must have the same presentation status as other virtual disks in the DR group. With some
versions of controller software, the virtual disk must be presented to a host. See storage
systems
Controller software features - remote replication . See also virtual disks Presentation .
Redundancy (Vraid) levels
Vraid is an HP term for implementing RAID storage (Redundant Array of Independent Disks). Virtual
disks with HP Vraid use three key RAID methods: data striping, data mirroring, and parity error
checking.
Data striping improves speed by performing virtual disk I/O with an entire group of physical disks
at the same time. Data mirroring provides data redundancy by storing data and a copy of the
data. Parity error checking provides automatic detection and correction if corruption of a physical
disk occurs. Unlike traditional RAID, all HP P6000 Vraid levels distribute data across all available
physical disks.
The redundancy (Vraid) level for a virtual disk determines the virtual disk's availability (data
protection) and influences its I/O performance. Once a virtual disk is created, its Vraid type cannot
be changed.
Vraid levels are:
•
Vraid0. Vraid0 (striping) and is optimized for speed and disk space utilization but does not
provide any redundancy.
IMPORTANT: HP does not recommend using Vraid0 when high availability is required.
•
Vraid1. Vraid1 (striping with mirroring) is optimized for speed and high data redundancy. A
Vraid1 virtual disk can automatically recover (reconstruct) from the failure of one physical
disk. Vraid1 uses about twice the physical disk space than Vraid0.
•
Vraid5. Vraid5 (striping with parity) is optimized for speed, disk space utilization, and moderate
redundancy. A Vraid5 virtual disk can automatically recover (reconstruct) from the failure of
one physical disk. Vraid5 uses about 20% more physical disk space than Vraid0.
•
Vraid6. Vraid6 (striping with dual parity) is optimized for speed and the highest redundancy.
A Vraid6 virtual disk can automatically recover (reconstruct) from the concurrent failure of two
physical disks. Vraid6 uses about 33% more physical disk space than Vraid0. Vraid6 support
is dependent on the controller software version. See the HP P6000 Enterprise Virtual Array
Compatibility Reference.
Disk groups with large physical disks
IMPORTANT: If a disk group includes large physical disks (for example, 1 TB or larger), HP
recommends using Vraid6 for the virtual disks.
The recovery (reconstruction) time for virtual disks increases with the size of the physical disks in
the disk group. With Vraid1 or Vraid5, a second physical disk failure during the longer recovery
time could prevent a complete recovery. The use of Vraid6 reduces the risk.
Snapclones
Snapclone replication instantly creates an independent, point-in-time copy of a virtual disk. The
copy begins as a fully allocated snapshot, and then automatically becomes an independent virtual
disk. The copy is called a snapclone. See also virtual disks
Snapclone FAQ and Snapclone
guidelines .
Virtual disk concepts 269