Dahua HCVR8204A-S3, User Manual, Page: 441 / 446

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Appendix H RAID Introduction
Appendix H-1 About RAID
RAID is an abbreviation for Redundant Array of Independent Disks.
It is to combine several independent HDDs (physical HDD) to form a HDD group (logic
HDD) to provide more storage capacity and data redundancy. Right now system
supports RAID0/RAID1/RAID5/RAID10. Each level has different data protection, data
usage and performance levels. Please refer to the following sheet for detailed information.
Appendix H-2 RAID Level
RAID
Level
Note Min HDD
Needed
RAID0

RAID0 has no redundancy and no verification function.
RAID0 has at least two HDDs. It uses two HDDs (or more)
to one and the data is saved in each HDD. The read-write
speed multiples since the bandwidth multiples.
Theoretically speaking, the speed of the RAID0 is the N of
the each HDD. The security level decrease N since the
data is saved in different HDD blocks instead of saving in
one HDD. That is to say, once any of the HDD is
damaged, system loses all data.

RAID0 just purely enhances read-write performance while
there is no data security guarantee. So, RAID0 is the most
vulnerable RAID type and there is no redundancy
function. Any HDD physical malfunction may affect all
data. So, RAID 0 is not for the environment of high data
security requirements.
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RAID1

RAID1 is a safe RAID mode. It realizes data redundancy
function via HDD data mirroring, so there are backup data
on these two HDDs respectively. When one HDD is
malfunction, system can read data from the other HDD.
So RAID 1 presents high redundant function. But the write
performance may be low since the data needs to be
written twice. RAID1 is an ideal option for the environment
of high security concern instead of the speed.

RAID1 has the highest unit cost in all the RAID types. But
it provides general high data security and operation
function. When one physical HDD is malfunction, system
can auto switch to the mirroring HDD to read and write
instead of rebuilding the invalid data.

When one HDD is malfunction, you can just replace the
damaged HDD. If the other HDD is damaged too before
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