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RAID-10 Array States
Configuration information of the array is held in a reserved area sector on each of the
first three member disk drives of the array. If fewer than two of these sectors can be
read or written, the array normally goes into the Offline state.
An important characteristic of RAID-10 is that the mirrored pairs can be located in
different sites in different power domains. The availability of a RAID-10 array is,
therefore, better than that of RAID-5 array. However, if both domains of a two-site
configuration are both operational, but communication is lost between the sites, it is
important to ensure that each system does not continue to operate on its own copy of
the array. Under this condition the data might not be consistent. To prevent this problem
from occurring, the first, third, and fifth member disk drives of the array are the primary
members; the second, fourth, and sixth member disk drives are the secondary
members. Access to at least one of the primary disk drives that contain the
configuration information is normally required for array operations to continue.
Therefore:
v If a network partition exists, the using system that has access to the primary
configuration disk drives continues to operate. The using system that has access to
only the secondary configuration disk drives cannot normally access the array.
v If the using system fails at the site that contains the secondary member disk drive,
the using system that has access to the primary configuration disk drives continues
to operate.
v If the using system that has access to the primary configuration disk drives fails and
the primary configuration disk drives also fail, only the site that contains the
secondary configuration disk drives remains operational. Normally, the using system
that is at the secondary site is not allowed access to the array. To allow this using
system access to the array, the user must use the RAID array configurator to set a
flag that allows the using system to operate on only the secondary disk drives.
A RAID-10 array can be in one of several states. A knowledge of those states is useful
when you are configuring your arrays. The states are described here.
Good State
A RAID-10 array is in the Good state when:
v All the member disk drives of that array are present.
v No member disk drive is deconfigured.
v Read and write operations can be done on the array.
v No rebuilding operations need to be done.
The array is fully protected from the loss of multiple member disk drives if one copy of
the mirrored data is still available. Some unsynchronized records might still be under
repair.
Exposed State
A RAID-10 array is in the Exposed state when member disk drives are missing but still
configured. Read and write operations can be performed on the array, although write
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User's Guide and Maintenance Information
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