HP AD510A - StorageWorks Modular Smart Array 1500 cs 2U Fibre Channel SAN Attach Controller Shelf Hard Drive Installation Manual page 26

Installation Procedures - All Deployments
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When planning and configuring the LUNs:
— In direct-connect environments or any environment using the ACU-CLI, a
minimum of one storage LUN on the MSA must be configured and set to
the appropriate host mode before connecting the MSA to the server.
— When determining how many hard drives to include in an array and how
many LUNs to create from that array, consider the I/O load of the data
that will be stored on those LUNs, and, also consider that rebuild and
expansion times increase with the number of drives.
— Optimize performance and redundancy by striping the drives in the array
across separate storage enclosures on different SCSI buses, especially in
mirrored environments using RAID 1 or RAID 1+0.
— In general, striping an array across many hard drives increases the total
throughput on that array and delivers better I/O performance, but there is
a performance trade-off when an array is divided into multiple LUNs. Too
many LUNs on the same group of hard drives causes more drive seeking
and a loss of throughput.
— Customize the RAID level and striping method to the type of data that
will be stored on the LUN. For example, depending on the number of
drives included in an array, the ACU may suggest RAID 6 (ADG) as the
default RAID level, which offers a high level of fault tolerance and usable
disk capacity, but at a significant cost to I/O performance. For comparable
fault tolerance but higher performance, consider using RAID 1+0 when
fault tolerance is desired and performance is more important than usable
capacity. Reserve RAID 6 for situations when fault tolerance is desired,
but usable capacity is more important than performance.
— Set the ratio of read cache to write cache to prioritize writing in RAID 1,
RAID 1+0, RAID 5, and RAID 6 (ADG) configurations to improve
non-random write performance.
— Set the controller rebuild priority to medium or high to minimize
exposure during a drive rebuild. During a drive rebuild, limit I/O activity
from the attached servers.
HP StorageWorks 1500 Modular Smart Array Installation Guide