Verbatim 2-Disk RAID USB and eSATA External Hard Drive User Manual page 8

RAID 0
(Also called Striping) distributes data across both disks in a way which
can improve throughput, while retaining full capacity. However, in case
of possible failure of either disk, all data will be lost and the array will
no longer mount to your computer. Available capacity is the combined
capacity of both drives.
If either disk fails in RAID 0 then the LED of the failed drive will change
to RED.
RAID 1
(Also called Mirroring) stores a duplicate set of data onto both disks, so that
if one disk fails all data can be recovered from the other disk.
Available capacity is equal to that of only one of the two included drives.
If either disk fails in RAID 1, then the LED corresponding to the failed disk
will change to RED. The remaining operational disk can continue to be used
until the failed disk has been replaced. However, in this instance there is no
longer any data protection provided by the second, failed drive.
If you have been using RAID 1 mode and there is a subsequent failure of
either of the two drives, you can disassemble the enclosure and replace
the failed drive with a new drive. After reassembling the enclosure, leave it
disconnected from your computer and power it up. When the new drive is
detected during the power-on sequence, the full data of the original drive
will be rebuilt onto the new drive. This rebuilding procedure can take many
hours (more than 5!) to complete. During the rebuilding procedure, the
LED of the original good drive will fl ash BLUE, while the LED of the new
replacement drive will fl ash RED. After the array has rebuilt successfully
both LEDs will change to BLUE.
Concatenation
(RAID Mode Switch Setting = "BIG") combines both physical disk drives
into a single virtual disk. Available capacity is the combined capacity of
both drives.
This mode provides no data redundancy. If either disk fails in Concatenation
mode, then the array will no longer mount to your computer.
If either disk fails in Concatenation mode, then the LED corresponding to
the failed disk will change to RED.
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