HP STORAGEWORKS ALL-IN-ONE STORAGE SYSTEM User Manual page 74

RAID level
RAID 1 – Mirroring
RAID 1+0 – Mirroring and Striping
RAID 5 – Distributed Data Guarding
RAID 6– Advanced Data Guarding
(ADG)
Setting a percent full warning threshold
To receive a warning alert when storage capacity reaches a specified limit, set the percent full warning
threshold. You can set a warning threshold for any application component, user-defined application,
and shared folder that ASM manages. An iSCSI LUN application will not have a warning threshold.
By default, the warning threshold is set to 80%. To change it, enter a new percent value on the
Advanced window.
74 Hosting storage for applications and shared folders
Description
that holds the data fails. However, because no logical drive capacity
is used for redundant data, this method offers the best capacity. This
method offers the best processing speed by reading two stripes on
different hard drives at the same time and by not having a parity
drive.
Offers a good combination of data protection and performance. RAID
1 or drive mirroring creates fault tolerance by storing duplicate sets
of data on a minimum of two hard drives. There must be an even
number of drives for RAID 1. RAID 1 and RAID 1+0(10) are the most
costly fault tolerance methods because they require 50 percent of the
drive capacity to store the redundant data. RAID 1 mirrors the contents
of one hard drive in the array onto another. If either hard drive fails,
the other hard drive provides a backup copy of the files and normal
system operations are not interrupted.
Offers the best combination of data protection and performance. RAID
1+0 or drive mirroring creates fault tolerance by storing duplicate sets
of data on a minimum of four hard drives. There must be an even
number of drives for RAID 1+0. RAID 1+0(10) and RAID 1 are the
most costly fault tolerance methods because they require 50 percent
of the drive capacity to store the redundant data. RAID 1+0(10) first
mirrors each drive in the array to another, and then stripes the data
across the mirrored pair. If a physical drive fails, the mirror drive
provides a backup copy of the files and normal system operations are
not interrupted. RAID 1+0(10) can withstand multiple simultaneous
drive failures, as long as the failed drives are not mirrored to each
other.
Offers the best combination of data protection and usable capacity
while also improving performance over RAID 6. RAID 5 stores parity
data across all the physical drives in the array and allows more
simultaneous read operations and higher performance than data
guarding. If a drive fails, the controller uses the parity data and the
data on the remaining drives to reconstruct data from the failed drive.
The system continues operating with a slightly reduced performance
until you replace the failed drive. RAID 5 can only withstand the loss
of one drive without total array failure. It requires an array with a
minimum of three physical drives. Usable capacity is N-1 where N is
the number of physical drives in the logical array.
Offers the best data protection and is an extension of RAID 5. RAID
6 uses multiple parity sets to store data and can therefore tolerate up
to 2 drive failures simultaneously. RAID 6 requires a minimum of 4
drives and is available only if the controller has an enabler. Writer
performance is lower than RAID 5 due to parity data updating on
multiple drives. It uses two disk for parity; its fault tolerance allows
two disks to fail simultaneously. Usable capacity is N-2 where N is
the number of physical drives in the logical array.