HP P4000 HP Smart Array SAS controllers for Integrity servers support guide - Page 24

Fault management in supported RAID configurations

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that predict imminent physical disk failure due to mechanical causes, including the condition of the read/write head, the seek error rate, and the spin-up time. When a threshold value is exceeded for a factor, the disk sends an alert to the controller that failure is imminent. Thus, you can back up data and replace the disk drive before failure occurs. NOTE: An online spare does not become active and start rebuilding when an imminent failure alert is sent, because the degraded disk has not failed yet and is still online. The online spare is activated only after a disk in an array fails. Drive failure alert features Interim data recovery Recovery ROM Sends an alert message to Event Monitoring Services (EMS) when a physical disk or a logical drive fails. Occurs if a disk fails in a fault-tolerant configuration. A redundancy feature that ensures continuous system availability by providing a backup ROM. This feature protects against corruption of a ROM image. For example, if a power fluctuation occurs during a ROM upgrade, the ROM image could be corrupted. In this instance, the server restarts using the remaining good copy of the ROM image. When you upgrade the ROM, the inactive image (the one not being used by the system) is upgraded. There is not normally a noticeable difference in operation. However, when you use Recovery ROM for the first time, both ROM images are upgraded, causing a boot delay of about 60 seconds. Fault management in supported RAID configurations If a physical disk fails in RAID 1, 1+0, 5, 50, ADG, or 60, the system still processes I/O requests, but at a reduced performance level. Replace the failed physical disk as soon as possible to restore performance and full fault tolerance for the logical drive it belongs to. The risk of continuing operations without replacing a failed physical disk varies depending on the RAID level that has been configured: RAID 1 RAID 1 is configured with a single mirrored pair of disks. If one physical disk fails, the remaining disk in the mirrored pair can still provide all data. RAID 1+0 A RAID 1+0 configuration has a minimum of four physical disks and the total number of physical disks is divisible by two to support mirrored pairs. In RAID 1+0, if a physical disk fails, the remaining disk in a mirrored pair still provides all data on the failed disk. Several physical disks in an array can fail without incurring data loss, as long as no two failed physical disks belong to the same mirrored pair. RAID 5 A RAID 5 configuration has a minimum of three physical disks, plus one or more online spares; one disk is used for a single parity scheme to rebuild data if a physical disk fails. If a disk fails, data is recovered using a parity formula and is typically written to an online spare disk. If a second disk fails before the data from the initial disk 24 Controller overview

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that predict imminent physical disk failure due to
mechanical causes, including the condition of the
read/write head, the seek error rate, and the spin-up time.
When a threshold value is exceeded for a factor, the disk
sends an alert to the controller that failure is imminent.
Thus, you can back up data and replace the disk drive
before failure occurs.
NOTE:
An online spare does not become active and start
rebuilding when an imminent failure alert is sent, because
the degraded disk has not failed yet and is still online. The
online spare is activated only after a disk in an array fails.
Drive failure alert features
Sends an alert message to Event Monitoring Services (EMS)
when a physical disk or a logical drive fails.
Interim data recovery
Occurs if a disk fails in a fault-tolerant configuration.
Recovery ROM
A redundancy feature that ensures continuous system
availability by providing a backup ROM. This feature
protects against corruption of a ROM image.
For example, if a power fluctuation occurs during a ROM
upgrade, the ROM image could be corrupted. In this
instance, the server restarts using the remaining good copy
of the ROM image. When you upgrade the ROM, the
inactive image (the one not being used by the system) is
upgraded.
There is not normally a noticeable difference in operation.
However, when you use Recovery ROM for the first time,
both ROM images are upgraded, causing a boot delay of
about 60 seconds.
Fault management in supported RAID configurations
If a physical disk fails in RAID 1, 1+0, 5, 50, ADG, or 60, the system still processes I/O requests,
but at a reduced performance level. Replace the failed physical disk as soon as possible to restore
performance and full fault tolerance for the logical drive it belongs to.
The risk of continuing operations without replacing a failed physical disk varies depending on
the RAID level that has been configured:
RAID 1
RAID 1 is configured with a single mirrored pair of disks. If one
physical disk fails, the remaining disk in the mirrored pair can still
provide all data.
RAID 1+0
A RAID 1+0 configuration has a minimum of four physical disks
and the total number of physical disks is divisible by two to support
mirrored pairs. In RAID 1+0, if a physical disk fails, the remaining
disk in a mirrored pair still provides all data on the failed disk.
Several physical disks in an array can fail without incurring data
loss, as long as no two failed physical disks belong to the same
mirrored pair.
RAID 5
A RAID 5 configuration has a minimum of three physical disks,
plus one or more online spares; one disk is used for a single parity
scheme to rebuild data if a physical disk fails. If a disk fails, data is
recovered using a parity formula and is typically written to an online
spare disk. If a second disk fails before the data from the initial disk
24
Controller overview