QNAP VS-2004L en - Manual (Page 172)

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Single Disk Volume
Each hard disk drive is used as a
standalone disk. If a disk is damaged, all
the data will be lost.
JBOD (Just a bunch of disks)
JBOD is a collection of hard disk drives
that does not offer any RAID protection.
The data are written to the physical disks
sequentially. The total storage capacity
equals to the sum of the capacity of all the
member drives.
RAID 0 Striping Disk Volume
RAID 0 (striping disk) combines 2 or more
hard disk drives into one larger volume.
The data is written to the hard disk drives
without any parity information and no
redundancy is offered.
The total storage capacity equals to the
sum of the capacity of all the member
drives.
RAID 1 Mirroring Disk Volume
RAID 1 duplicates the data between two
hard disk drives to provide disk mirroring.
To create a RAID 1 array, a minimum of 2
hard drives are required.
The storage capacity of a RAID 1 disk
volume is equal to the size of the smallest
hard drive.