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Glossary 143
Mirroring
The process of providing complete redundancy using two physical disks, by
maintaining an exact copy of one physical disk’s data on the second physical
disk. If one physical disk fails, the contents of the other physical disk can be
used to maintain the integrity of the system and to rebuild the failed physical
disk.
Multi-bit ECC Errors
ECC errors are errors that occur in the memory, which can corrupt cached data
so that it has to be discarded. ECC double-bit errors are serious, as they result in
corrupted data and data loss. In case of double-bit ECC errors, contact Dell
Technical Support.
Multi-pathing
PERC 6 firmware provides support for detecting and using multiple paths
from the RAID controllers to the SAS devices that are in enclosures.
Devices connected to enclosures have multiple paths to them. With edundant
paths to the same port of a device, if one path fails, another path can be used
to communicate between the controller and the device.
N
Non Read Ahead
Non read ahead is a cache read policy. If you select Non read ahead in the BIOS
Configuration Utility, the controller does
not
read sequentially ahead of
requested data and store the additional data in cache memory, anticipating that
the data is needed soon. Non read ahead is most effective when accessing
random data.
Non Redundant Virtual Disk
A non-redundant virtual disk is one which does not have redundant data on
physical disks that can be used to rebuild a failed physical disk. A RAID 0 virtual
disk consists of data striped across the physical disks, without disk mirroring or
parity to provide redundancy. This provides for high data throughput but offers
no protection in case of a physical disk failure.
Dell_PERC6.1_UG.book Page 143 Wednesday, April 15, 2009 4:18 PM