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5-2 Intel® Server RAID Controller U3-1 User’s Manual Rev 1.0
RAID Features
5.1.3.2 Online RAID Reconfiguration
SRCU31 can migrate an existing RAID volume to a new RAID level and/or strip size. Online
RAID reconfiguration can prove helpful during performance tuning activities as well as in the
event that additional physical disks are added to a RAID subsystem, for example, the addition of a
third disk to a RAID subsystem that currently has a two disk RAID 1 volume. With the addition of
this third disk, you have the option of adding this disk to your existing RAID volume and migrating
the RAID level from 1 to 5.
RAID transformation is only permitted to begin if all volumes to be transformed are in normal
mode. During the transformation, they are protected against data loss from a single disk failure
provided that neither the source nor destination RAID levels are 0. In the case of a single disk
failure, the RAID volume in a transforming state transitions from normal mode to degraded mode.
When the transformation is completed, the volume transitions to an idle state in degraded mode and
if a global hot spare were present, it would transition to a rebuilding state in degraded mode. When
there is more than one RAID volume on an array, certain types of transformations may be applied
to individual RAID volumes, while other types of transformations must be applied to all RAID
volumes on the array.
Some transformations may be physically impossible due to insufficient disk capacity or an
incorrect number of physical disks in the destination array. The SRCU31 Storage Console performs
background validation to determine which migrations are possible.
5.1.3.3 Online Volume Migration
Online Volume Migration allows the user to change a volume's RAID level or stripe size while the
server is online and the volume is in-use. Since the subsystem (the IOP, the secondary PCI bus, the
volume itself and the SCSI bus) incurs a load during a migration or during a rebuild of a degraded
volume, the SRCU31 allows the user to select the migration priority (low, medium, high).
Adjusting migration priority appropriately balances volume access and rebuild tasks during the
volume's migration or volume rebuild.
Migration Priority determines the amount of time that the I/O processor in your server/workstation
spends on migrating from one RAID level to another. Migration priority can be set at low, medium
or high. As with volume initialization, a system reboot does not require the rebuild process to
restart from the beginning. The settings are defined as:
• Low - the I/O processor spends a majority of its time handling normal input/output activities of
the server/workstation while spending a small amount of time on the migration. This setting
has the smallest affect on the performance of the array.
• Medium - the I/O processor spends an equal amount of time processing the migration while
spending the other half of its time handling normal input/output activities of the server/
workstation.
• High - the I/O processor spends most of its time handling the migration. This setting will
impact performance of the array while the migration is taking place.
5.1.3.4 Online Capacity Expansion Without Reboot
An array is a group of disks containing 1 or more RAID volumes. An array is implicitly created
whenever a RAID volume is created on a group of unused disks. Data from that RAID volume is
evenly spread across all disks in the array. If an array has unused capacity, additional RAID
volumes may be created on that array. The data from additional RAID volumes is likewise evenly
spread across all the disks in the group.