Dell Precision T3400 (Late 2007) - Manual (Page 45)

About RAID Configurations
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If a drive failure occurs, subsequent read and write operations are directed to
the surviving drive. A replacement drive can then be rebuilt using the data
from the surviving drive.
NOTE:
In a RAID level 1 configuration, the size of the configuration is equal to the
size of the smallest drive in the configuration.
RAID Level 5
RAID level 5 uses a data-staging storage technique known as data parity.
When data is written to the primary drive, the data is duplicated on at least
three other drives. Unlike a RAID level 1 configuration which writes to one
other volume that acts as a data mirror, a RAID level 5 configuration writes
data to each drive in increments, placing data from each segment across
multiple drives. A RAID level 5 configuration has higher data-access rates,
but requires more storage space than a RAID level 0 or RAID level 1
configuration.
hard drive 1
segment 1
segment 2
segment 3
hard drive 2
segment 4
segment 5
segment 6
segment 1 duplicated
segment 2 duplicated
segment 3 duplicated
segment 4 duplicated
segment 5 duplicated
segment 6 duplicated
serial ATA RAID
configured for
RAID level 1