Related Topics; About Vdisks - HP P2000 G3 Reference Manual

NOTE: To secure the storage system, set a new password for each default user.

Related topics

• Configuring user accounts

About vdisks

A vdisk is a "virtual" disk that is composed of one or more disks, and has the combined capacity of those
disks. The number of disks that a vdisk can contain is determined by its RAID level. All disks in a vdisk must
be the same type (SAS or SATA, small or large form-factor). A maximum of 16 vdisks per controller can
exist.
A vdisk can contain different models of disks, and disks with different capacities. For example, a vdisk can
include a 500-GB disk and a 750-GB disk. If you mix disks with different capacities, the smallest disk
determines the logical capacity of all other disks in the vdisk, regardless of RAID level. For example, if a
RAID-0 vdisk contains one 500-GB disk and four 750-GB disks, the capacity of the vdisk is equivalent to
approximately five 500-GB disks.
Each disk has metadata that identifies whether the disk is a member of a vdisk, and identifies other
members of that vdisk. This enables disks to be moved to different slots in a system; an entire vdisk to be
moved to a different system; and a vdisk to be quarantined if disks are detected missing.
In a single-controller system, all vdisks are owned by that controller. In a dual-controller system, when a
vdisk is created the system automatically assigns the owner to balance the number of vdisks each controller
owns; or, you can select the owner. Typically it does not matter which controller owns a vdisk.
In a dual-controller system, when a controller fails, the partner controller assumes temporary ownership of
the failed controller's vdisks and resources. If a fault-tolerant cabling configuration is used to connect the
controllers to drive enclosures and hosts, both controllers' LUNs are accessible through the partner.
When you create a vdisk you can use the default chunk size or one that better suits your application. The
chunk size is the amount of contiguous data that is written to a disk before moving to the next disk. After a
vdisk is created its chunk size cannot be changed. For example, if the host is writing data in 16-KB
transfers, that size would be a good choice for random transfers because one host read would generate
the read of exactly one disk in the volume. That means if the requests are random-like, then the requests
would be spread evenly over all of the disks, which is good for performance. If you have 16-KB accesses
from the host and a 64-KB block size, then some of the hosts accesses would hit the same disk; each chunk
contains four possible 16-KB groups of data that the host might want to read, which is not an optimal
solution. Alternatively, if the host accesses were 128 KB, then each host read would have to access two
disks in the vdisk. For random patterns, that ties up twice as many disks.
When you create a vdisk you can also create volumes within it. A volume is a logical subdivision of a
vdisk, and can be mapped to controller host ports for access by hosts. The storage system presents only
volumes, not vdisks, to hosts.
You can create vdisks with or without volumes by using the Provisioning Wizard, or you can create vdisks
manually.
Best practices for creating vdisks include:
• To maximize capacity, use disks of similar size.
• For greatest reliability, use disks of the same size and rotational speed.
• For storage configurations using many disks, create a few vdisks each containing many disks instead of
many vdisks each containing a few disks.
• To maximize capacity and disk usage (but not performance), you can create vdisks larger than 2 TB
and divide them into multiple volumes each having a capacity of 2 TB or less. This increases the usable
capacity of storage configurations by reducing the total number of parity disks required when using
parity-protected RAID levels. This differs from using a volume larger than 2 TB, which requires specific
support by the host operating system, I/O adapter, and application.
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HP StorageWorks P2000 G3 MSA System SMU Reference Guide 21