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© 2008 Apacer Technology Inc Rev 0.2 (Preliminary)
T e RAID Processor supports a definition of Safe (RAID-1) set. T e HBA (Host Bus Adapter) does not need
to know anyt ing about t e p ysical arrangement of t e data. To t e HBA, t e virtualized drive be ind RAID
Processor is a normal drive t at just appens to be safer (fault tolerant). All error andling and Data rebuild is
managed by t e RAID Processor. T e two p ysical partitions used for mirroring must reside on two different
p ysical disks, as t ere is no benefit of mirroring t e data on t e same drive. T e advantage of mirroring is
essentially safeguarding t e data in case of a single p ysical drive failure. For a read operation, t e RAID
Processor decides w ic p ysical partition to read from and for write, t e data is written to bot drivers. Note:
T ere is no benefit of performance due to mirroring. Often t e performance may suffer slig tly, as t e data will
be transferred to t e least common denominator of t e two p ysical drives. T e two p ysical partitions used
for mirroring must reside on two different p ysical disks, as t ere is no benefit of mirroring t e data on t e
same drive.
2 8 RAID-1 Racing
T e Storage Processor improves t e speed of RAID 1 (SAFE) mode by introducing RAID 1 drive racing.
W en reading a sector, bot mirrored drives race and t e first one to get t e data supplies t e information,
lowering t e average seek time.
2 9 Sector Recovery and Disk Rebuild
For Safe (RAID-1) volumes, t e firmware implements t ree additional features to make t e data more reliable,
Sector Recovery, Disk Rebuild and Disk Verify.
2 9 1 Sector Recovery
For Safe (RAID-1) volumes, at any time, if t e Storage Processor detects any read or write error, it
automatically (wit out ost intervention):
Take t e P ysical Partition Off-line
Attempt to copy t e respective data from t e ot er mirrored Partition (if available).
If t e re-write is successful, t en t e problem is solved before it got to be catastrop ic.
Bring t e P ysical Partition On-Line.
In case t e problem still persists after re-write (Read-Verify fails), t en it is assumed t at P ysical Partition on
t e P ysical Disk is bad (and all spare sectors implemented by t e HDD itself are depleted). In t is event, t is
P ysical Partition (wit Error) will stay off-line. Ot er P ysical Partitions on t is HDD are still good and stay
on-line. In addition, t at HDD’s LED will s ow t e Error State. In t e rare case, if t ere is anot er sector
