HP X1000 Network Storage Systems - Manual (Page 26)

Description RAID level
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.
RAID 1+0 – Mirroring and Striping
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 sim-
ultaneous read operations and higher performance than data guard-
ing. 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 minim-
um of three physical drives. Usable capacity is N-1 where N is the
number of physical drives in the logical array.
RAID 5 – Distributed Data Guarding
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.
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.
After you set a warning threshold, ASM changes the status indicator for the application component,
user-defined application, or shared folder when this threshold has been surpassed. This is a warning
only; no hard limits are enforced on storage capacity as a result of setting this value. The warning is
visible in these places:
• A yellow warning icon appears on the application component, user-defined application, or shared
folder icon in the content pane.
• As an alert in the Properties window.
Hosting storage for applications and shared folders 26