HP NetServer AA 4000 Reference Manual page 12

HP NetServer AA
1-6
allowing for the fail through performance should anything happen to
one of the CEs.
I/O Processors
The other two NetServers take the roles of I/O Processors (IOPs).
Within the AA 4000 software the IOPs are numbered IOP1 and
IOP2. An IOP performs all I/O operations on behalf of the CE. It
contains the hard disk drives necessary for storing its own copy of
Windows NT, the CE's copy of Windows NT, the applications
installed on the CEs (applications for the array), and all of the needed
data. It also has all of the network cards necessary for client access.
In a PCI slot in the IOP is a MIC. Through the SSDLs, the IOP's
MIC can communicate with either one of the CEs. Typically it only
communicates with one of the CEs.
It is necessary for the IOPs to boot first before the CEs can boot up.
At least one IOP has to be ready with disks available in order for a
CE to have a disk from which it can boot. When the IOP is
operational, the NT administrative tools only see one logical disk,
the one with its own copy of Windows NT. The rest of the disks
have been "redirected" to the ownership of the CEs (redirection will
be covered later in this chapter).
In effect, what is happening is whenever the CE has an I/O operation
to perform, the AA 4000 software intercepts the I/O request Window
NT has made, passes it to the MIC, the MIC passes it to the MIC in
the IOP, then the IOP executes the I/O. This happens in the IOP as if
the I/O operation originated in the IOP's copy of Windows NT when
in fact it was "inserted" by the AA 4000 software and MICs. When
the I/O operation is complete, the "results" are sent back through the
MICs to the processor and cache of the CEs.
Tuple
Tuple 1 Tuple 2
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