Spare Drives; Lun Sizing (Capacity) - HP StorageWorks Modular Smart Array 1500 cs Installation Manual

Installation Procedures - All Deployments

Spare drives

HP recommends including spare drives in your LUNs.
Spares are disks that are not active members of any particular LUN, but have been
configured to be used in the event that a disk in one of the LUNs should fail. If a
spare is present and a physical 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 disks to reconstruct the data onto the spare
drive.

LUN sizing (capacity)

When planning for optimal file serving performance, the number of hard drives
necessary to maintain an optimum performance level must be determined.
As a general rule, the greater the number of drives that are included in a LUN, 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 a LUN, the higher the probability of one or more disk failures
in that LUN.
22 Modular Smart Array 1500 cs Installation Guide