Fault Tolerant Features - Intel AFCSASRISER User Manual

Fault Tolerant Features

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Intel RAID Software User's Guide
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Hot spares can be set as global or dedicated. A global hot spare automatically comes
online to replace the first drive to fail on any array or disk group on the controller. A
dedicated hot spare is assigned to a specific array or disk group and only comes online to
rebuild this specific failed array or disk group. A hot spare only comes online if it is the
same size or larger than the failing drive (see drive coercion below), and if a drive has
been marked as failed. If a drive is removed (and marked as failed) within a virtual drive,
the hot spare automatically comes online. However, there must be disk activity (I/O to
the drive) in order for a missing drive to be marked as failed.
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Drive coercion refers to the ability of the controller to recognize the size of the physical
drives connected and then force the larger drives to use only the amount of space
available on the smallest drive. Drive coercion allows an option to map out a reserved
space to compensate for slightly smaller drive sizes that may be added later. The default
is set to 1 GB. The coercion algorithm options are:
— None: No coercion of size.
— 128 MB: The software rounds the drive capacity down to the next 128 MB boundary
and then up to the nearest 10 MB until the coerced capacity is larger than the actual
drive size. It is then reduced by 10 MB.
— 1 GB: The software rounds the drive capacity down to the nearest 1 GB boundary
and then down by 1 MB. This corresponds to the terms most drive manufacturers
use.
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Configuration on Disk (COD) and NVRAM (Non-volatile Random Access Memory)
storage of array and disk group configuration information. Array and disk group
configuration information is stored both on the hard drive (COD) and in NVRAM. This
helps protect against loss of the configuration due to adapter and/or drive failure.
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Failed drives are automatically detected and a transparent rebuild of the failed array
automatically occurs using a hot-spare drive.
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Support for SAF-TE (SCSI Accessed Fault-Tolerant Enclosure) enabled enclosures
allows enhanced drive failure and rebuild reporting via enclosure LEDs (Light-Emitting
Diodes); support also includes hot swapping of hard drives.
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A battery backup for cache memory is available as an option. RAID controller firmware
automatically checks for the presence of the battery module, and if found, allows the
write back cache option. The adapter continuously tracks the battery voltage and reports
if the battery is low. If low, the battery is first given a fast charge to replenish the charge
and is then given a trickle charge to keep it at an optimal power level. Adapters that
support the battery module include a "dirty cache" LED; when power is lost to the
system and data remains in the cache memory that has not been written to disk, the LED
signals that this operation needs to be completed. Upon reboot, the data in memory can
then write to the hard disk drive.
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Although I/O performance may be lower, hard disk drive write-back cache is disabled by
default because data can potentially be lost if a power outage occurs. Enabling the HDD
write-back cache may improve performance, but when enabled, you should use a UPS
(Uninterruptible Power Supply) device to prevent data loss during power outages.
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Battery life is about three years. You should monitor the battery health and replace when
needed.
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