6760 ServerNet/DA Manual

Introduction to the 6760 ServerNet/DA
6760 ServerNet/DA Manual—424879-003
1-10
Disk Configuration for Fault Tolerance
Disk Configuration for Fault Tolerance
The 6760 adapter logic board is shipped with up to four SACs installed on it. If you
want full fault tolerance with magnetic disk drives, you must order at least two 6760
adapters.
Up to 8 disks in one disk module can be controlled by 6761 F-SACs.
The external disks and 6760 adapters in your system can be configured for various
levels of fault-tolerance:
•
6760 Adapters in Noninterleaved Enclosures
•
6760 Adapters in Interleaved Enclosures
Most NonStop S-series systems support a maximum of two 6760 adapters in each
system enclosure. For the exception to this rule, refer to Four 6760 Adapters in a
NonStop S700 System on page 1-13.
6760 Adapters in Noninterleaved Enclosures
External disks can be connected to two 6760 adapters installed in the same system
enclosure. This configuration can tolerate the failure of a ServerNet fabric. To ensure
this level of fault tolerance, see Balance 6760 Adapters Between Slots and Balance
6760 Adapters Across Enclosures, following.
Balance 6760 Adapters Between Slots
To ensure fault-tolerance, you should install one 6760 adapter in an even-numbered
slot and the other 6760 adapter in an odd-numbered slot.
You should balance the 6760 adapters between even-numbered slots and odd-
numbered slots, because this makes disk drives less vulnerable to a single point of
failure (a slot or fabric failure). Because the 6760 adapter accesses only one fabric,
which fabric it accesses depends on the slot in which it is installed. It accesses the
X fabric when installed in an odd-numbered slot, and it accesses the Y fabric when
installed in an even-numbered slot. Therefore, you ensure that a disk can be accessed
even if a slot or fabric fails, if all of the following are true:
•
You balance the adapters by distributing them evenly between odd-numbered and
even-numbered slots.
•
You configure the primary path of the disk drive through the adapter in the odd-
numbered slot.
•
You configure the backup path of that disk drive through the adapter in the even-
numbered slot.