Supported Raid Levels; Raid 5 - IBM SAS RAID Series Manual

Supported RAID levels

The RAID level of a disk array determines how data is stored on the disk array and the level of
protection that is provided.
If a part of the RAID system fails, different RAID levels help to recover lost data in different ways. If a
single drive fails within an array, the array controller can reconstruct the data for the failed disk by using
the data stored on other hard drives within the array. This data reconstruction has little or no impact to
current system programs and users. The controller supports RAID levels 5 and 6 as well as system
mirroring. Not all controllers support all RAID levels. Each RAID level supported by the controller has its
own attributes and uses a different method of writing data. The following information provides details
for each supported RAID level.
Related concepts
"PCI-X SAS RAID card comparison" on page 3
Use the table in this topic to compare the features of PCI-X SAS RAID cards for IBM i. There are also
images of adapters for you to view.
"PCIe SAS RAID card comparison" on page 6
Use the table in this topic to compare the features of a PCI Express (PCIe) SAS RAID cards for IBM i.
There are also images of adapters for you to view.
Related information
Device parity protection concepts

RAID 5

Learn how data is written to a RAID 5 array.
RAID 5 stripes data across all disks in the array. RAID level 5 also writes array parity data. The parity
data is spread across all the disks. For a RAID 5 array of three disks, array data and parity information
are written in the following pattern:
Figure 8. RAID 5
If a disk fails in a RAID 5 array, you can continue to use the array normally. A RAID 5 array operating
with a single Failed disk is said to be operating in Degraded mode. Whenever data is read from a
Degraded disk array, the array controller recalculates the data on the Failed disk by using data and parity
blocks on the operational disks. If a second disk fails, the array will be placed in the Failed state and will
not be accessible.
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SAS RAID controllers for IBM i