User guide
Technical white paper | HP Enterprise Virtual Array Storage and VMware vSphere 4.x and 5.x configuration best practices
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Disk group provisioning
An EVA disk group is the largest storage object within the EVA storage virtualization scheme and is made up of a minimum
of eight physical disks for FC, SAS or FATA drives and 6 for SSD drives. Within a disk group, you can create logical units of
various sizes and RAID levels.
Notes
• An EVA RAID level is referred to as VraidX.
• The EVA array allows Vraid0, Vraid1, Vraid5, and Vraid6 logical units to coexist in the same disk group on the same
physical spindles.
• Not all EVA models support all disk drive types mentioned above.
• SSD drives require their own disk group.
• FATA drives require their own disk group.
• FC drivers require their own disk group.
• SAS drives require their own disk group.
When configuring an EVA disk group for vSphere 4.x and 5.x, keep in mind the following important factors:
• Formatted capacity
• Sparing overhead and drive failure protection level
• Application being virtualized
• Storage optimization requirements
Formatted capacity
Although disk capacity is typically referred to in round, integer numbers, actual storage capacity in an EVA is tracked in
binary form; thus, the formatted capacity of a drive may be slightly smaller than its nominal capacity. For example, a drive
with a nominal capacity of 146 GB provides 136.73 GB of formatted capacity, approximately 6.5% less.
Sparing overhead and drive failure protection level
Sparing overhead in an EVA array is defined as the amount of space that must be reserved to be able to recover from
physical disk failures within a disk group. Unlike other storage systems, which set aside specific disks as spare drives, the
EVA spreads the spare space
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across all the disks within a group. The EVA sparing implementation eliminates the possibility
of an assigned spare disk failing when it is needed for recovery.
The overhead created by sparing is calculated as follows:
In this formula, the value for disk drive failure protection level (Protection level) may be as follows:
• None
• Single – The disk group survives the failure of a single disk
• Double – The disk group survives the failure of two disks
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Also known as reconstruction space