Hard Drive Sizes And Types; Spare Drives; Array Sizing (Capacity) - HP AD510A - StorageWorks Modular Smart Array 1500 cs 2U Fibre Channel SAN Attach Controller Shelf Hard Drive Installation Manual

NOTE: For detailed information about the different RAID levels, see the HP Array Configuration
Utility User Guide. This guide is available on the Documentation CD and on the Technical
documentation page of the MSA1500 website: http://www.hp.com/go/msa1500cs.

Hard drive sizes and types

Hard drives in each enclosure and included in the same array should be the same size and type.
When drive sizes and types are mixed within a storage enclosure, the usable capacity and the
processing ability of the entire storage sub-system is affected.
When hard drives of different types or sizes are included in the same enclosure, the processing
characteristics of the entire enclosure are reduced to that of the slowest and smallest drive.
When hard drives of different sizes are included in a LUN, the LUN defaults to the smallest
individual drive size and capacity in the larger drives is unused.

Spare drives

HP recommends including spare drives in your LUNs.
Spares are hard drives that are not active members of any particular LUN, but have been configured
to be used in the event that a drive in one of the LUNs should fail. If a spare is present and a
physical hard drive fails, the spare automatically replaces the failed drive as a member of the LUN
and the process of rebuilding the information onto the spare automatically begins. The system uses
the mirrored or parity information from the other member drives to reconstruct the data onto the
spare.

Array sizing (capacity)

When planning for optimal file-serving performance, you must determine the number of hard drives
necessary to maintain an optimum performance level.
As a general rule, the greater the number of drives that are included in an array, the greater the
performance level that can be achieved. However, the performance considerations are offset by
fault tolerance considerations—the greater the number of drives in an array, the higher the
probability of one or more failures in that array.
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