Chassis Install Instructions (734751-001, March 2014)

Disk drive sizes and types
RAID arrays should be composed of disk drives of the same size and performance capability.
When drives are mixed within a disk enclosure, the usable capacity and the processing ability of
the entire storage subsystem is affected. For example, when a RAID array is composed of different
sized drives, the RAID array defaults to the smallest individual drive size, and capacity in the larger
drives goes unused.
Spare disks
Spares are disks that are not active members of any particular array, but have been configured
to be used when a disk in one of the arrays fails. If a spare is present, it will immediately be used
to begin rebuilding the information that was on the failed disk, using parity information from the
other member disks. During the rebuilding process, the array is operating in a reduced state and,
unless it is a RAID6 or RAID1+0 array, it cannot tolerate another disk failure in the same array. If
another disk fails at this time, the array becomes inaccessible and information stored there must
be restored from backup.
Following the rebuild of the data onto the spare and when a replacement drive is inserted to replace
the failed drive, the system will automatically transfer the data from the spare onto the replacement
drive and return the spare to an available-spare state. It is important to note that the process of
rebuilding the spare or the replacement drive must not be interrupted or the process will be aborted.
Some administrators have multiple spare disks, so that multiple arrays can experience failure and
successfully recover, before administrative intervention would be required to replace the spare or
failed disk. When assigning a spare to an array, the administrator chooses which arrays and how
many arrays are protected by that spare.
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, 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 disk failures in that array. The administrator must strike a balance between
performance and fault tolerance.
Array sizing
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, 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 disk failures in that array. The administrator must strike a balance between
performance and fault tolerance.
Preparing the site
Preparing your site includes:
• Providing adequate structural support
Calculate the total weight of your equipment and verify that your site can support the weight.
• Providing adequate clearance
Be sure to provide adequate clearance around the front and back of the racks. Provide at
least 63.5 cm (25 in) in the front of the rack to allow the doors to open fully and provide at
least 76.2 cm (30 in) in the rear of the rack to allow for servicing and airflow.
If there are unused spaces in your rack, attach blanking panels across those empty spaces to
force the airflow through the components instead of through the open spaces.
• Providing adequate and redundant sources of power
Make sure that you have two high-line power feeds installed near your computer. These two
power sources usually come from the same external power grid, but occasionally might
originate from different grids or even entirely different sources.
Preparing the site 11