To maximize the performance
of a volume group, you must select the appropriate RAID level. You can
determine the appropriate RAID level by knowing the read and write
percentages for the applications that are accessing the volume
group. Use the Performance page to obtain these percentages.
RAID levels and application performance
RAID relies on a series of
configurations, called levels, to determine how user and redundancy data is written and retrieved from
the drives. Each RAID level provides
different performance features. Applications with a high read
percentage perform well using RAID 5 volumes or RAID 6
volumes because of the outstanding read performance of the RAID
5 and RAID 6 configurations.
Applications with
a low read percentage (write-intensive) do not perform as well on
RAID 5 volumes or RAID 6 volumes. The degraded
performance is the result of the way that a controller writes data and redundancy data to the drives in a RAID 5
volume group or a RAID 6 volume
group.
Select a RAID level based on the following information.
RAID 0
- Description
- Non-redundant, striping mode.
- How it
works
- RAID 0 stripes data
across all of the drives in the volume group.
- Data
protection features
- RAID 0 is not recommended
for high availability needs. RAID 0 is better for
non-critical data.
- If a single
drive fails in the volume group, all of the associated volumes
fail, and all data is lost.
- Drive
number requirements
- A minimum of one drive is required for RAID Level 0.
- RAID 0 volume groups can
have more than 30 drives.
- You can create a volume group that
includes all of the drives in the storage array.
RAID 1 or RAID 10
- Description
- How it
works
- RAID 1 uses disk mirroring
to write data to two duplicate disks simultaneously.
- RAID 10 uses drive striping to
stripe data across a set of mirrored drive pairs.
- Data
protection features
- RAID 1 and RAID 10 offer high performance
and the best data availability.
- RAID 1 and RAID 10 use drive mirroring to
make an exact copy from one drive to another drive.
- If one of the
drives in a drive pair fails, the storage
array can instantly switch to the other drive without any
loss of data or service.
- A single
drive failure causes associated volumes to become degraded. The
mirror drive allows access to the data.
- A drive-pair
failure in a volume group causes all of the associated volumes to
fail, and data loss could occur.
- Drive
number requirements
- A minimum of
two drives is required for RAID 1: one drive for the
user data, and one drive for the mirrored data.
- If you select
four or more drives, RAID 10 is automatically
configured across the volume group: two drives for user data, and
two drives for the mirrored data.
- You must have
an even number of drives in the volume group. If you do not have an
even number of drives and you have some remaining unassigned
drives, select Storage > Pools & Volume Groups to add additional
drives to the volume group, and retry the operation.
- RAID 1 and RAID 10 volume groups can have
more than 30 drives. A volume group can be created that includes
all of the drives in the storage array.
RAID 5
- Description
- How it
works
- User data and
redundant information (parity) are striped across the drives.
- The
equivalent capacity of one drive is used for redundant
information.
- Data
protection features
- If a single
drive fails in a RAID 5 volume group,
all of the associated volumes become degraded. The redundant
information allows the data to still be accessed.
- If two or
more drives fail in a RAID 5 volume group, all of
the associated volumes fail, and all data is lost.
- Drive
number requirements
- You must have
a minimum of three drives in the volume group.
- Typically,
you are limited to a maximum of 30 drives in the volume group.
RAID 6
- Description
- How it
works
- User data and
redundant information (dual parity) are striped across the
drives.
- The
equivalent capacity of two drives is used for redundant
information.
- Data
protection features
- If one or two
drives fail in a RAID 6 volume group,
all of the associated volumes become degraded, but the redundant
information allows the data to still be accessed.
- If three or
more drives fail in a RAID 6 volume group, all of
the associated volumes fail, and all data is lost.
- Drive
number requirements
- You must have
a minimum of five drives in the volume group.
- Typically,
you are limited to a maximum of 30 drives in the volume group.
Note: You cannot change the RAID level of a pool. System Manager automatically configures pools as
RAID 6.
RAID levels and data protection
RAID 1, RAID 5, and RAID 6 write redundancy
data to the drive media for fault tolerance. The redundancy
data might be a copy of the data (mirrored) or an error-correcting
code derived from the data. You can use the redundancy data to
quickly reconstruct information on a replacement drive if a drive
fails.
You configure a single RAID level across a single volume
group. All redundancy data for that volume group is stored within
the volume group. The capacity of the volume group is the aggregate
capacity of the member drives minus the capacity reserved for
redundancy data. The amount of capacity needed for redundancy
depends on the RAID level used.