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EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
The transmission codes also help to assist in detecting errors in
transmission. Finally, once the data has been received at the disk
drive (for writes) and decoded from the transmission codes, it will
then be further recoded using a very powerful linear block coding
algorithm before being stored on the disk’s magnetic surface. This
code has the ability to not only detect errors, but to also correct them
on the fly—ensuring that the data read from the drive at a later time
will be read perfectly.
Dual-initiator
feature
Symmetrix DMX systems have a dual-initiator feature that ensures
continuous availability of data in the unlikely event of a Symmetrix
disk management hardware failure. The dual-initiator feature does
not provide data availability in the event of a disk drive failure. This
feature works by having each of the four processors on the paired
disk directors shadow each other’s functions. For example, this
feature gives each processor the capability of servicing any or all of
the devices of the processor with which it is paired, should one of the
processors be unable to partially or fully service its own devices.
With the dual-initiator feature, for example, each of the four
processors and its LCC of Disk Director 1 is paired with a LCC and a
processor of Disk Director 16 (Figure 39 on page 169). Under normal
conditions, each disk director processor services its own disk drives.
If the sophisticated fencing mechanisms of the Symmetrix system
detect a failure on the disk director, the system reads from or writes to
the disk drives through the disk director processor’s shadowed
alternate path without interruption, and then notifies the EMC
Customer Support Center. When the source of the failure is corrected,
the Symmetrix system returns the I/O servicing of the two disk
director processors to their normal state.
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