Rosewill R2-RAID - Manual (Page 16)

Server RAID System [ R2-RAID ] User Manua
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RAID / SAFE50 ：It creates two
virtual volumes; one SAFE
volume and one BIG volume,
and should be used when you
need the high reliability for some
of your data but you don’t need
high reliability for the remainder
of your data. It reduces the cost of additional hard drives in operations
where non-critical data could be lost without severe consequences. If one
drive fails the SAFE volume is retrievable although the BIG volume is not.
When you replace the failed drive, the SAFE volume is automatically rebuilt
on to the replacement drive.
When using a SATA host connection, you must have a PM (Port Multiplier)
aware host adapter when using SAFE50 on the top level node of a
cascaded configuration so that ALL volumes can be detected by the host. If
your SATA host adaptor is not PM aware, then ONLY the SAFE volume will
be detected and the BIG volume will not be accessible. No such limitation
exists when using a USB host connection.
The size of the SAFE volume will be one-half of the size of one hard drive
(if they are equal) or one-half of the size of the smaller (if they are not equal).
The size of the BIG volume will be the combination of all remaining
capacities.
Drive A
250GB
Drive B
250GB
HD3206SRD
Port 0 Port 1
Safe
125GB
Equal hard drives
Drive A
250GB Drive B
750GB
HD3206SRD
Port 0 Port 1
Big
250GB
Safe
125GB
Drive B
750GB
Unequal hard drives