Dahua Technology IVSS, User Manual

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User's Manual
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Appendix 3 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).
Comparing with one HDD, RAID provides more storage capacity and data redundancy. The different
redundant arrays have different RAID level. Each RAID level has its own data protection, data
availability and performance degree.
RAID Level
RAID Level Description Min. HDD Needed
RAID0
RAID 0 is called striping.
RAID 0 is to save the continued data
fragmentation on several HDDs. It can process
the read and write at the same time, so its
read/write speed is N (N refers to the HDD
amount of the RAID 0) times as many as one
HDD. RAID 0 does not have data redundant, so
one HDD damage might result in data loss that
cannot be restored.
2
RAID1
It is also called mirror or mirroring.
RAID 1 data is written to two HDDs equally,
which guarantee the system reliability and can
be repaired. RAID 1 read speed is almost close to
the total volume of all HDDs. The write speed is
limited by the slowest HDD. At the same time,
the RAID 1 has the lowest HDD usage rate. It is
only 50%.
RAID5
RAID5 is to save the data and the corresponding
odd/even verification information to each HDD
of the RAID5 group and save the verification
information and corresponding data to different
HDDs. When one HDD of the RAID5 is damaged,
system can use the rest data and corresponding
verification information to restore the damaged
data. It does not affect data integrity.
3
RAID6
Based on the RAID5, RAID6 adds one odd/even
verification HDD. The two independent odd/even
systems adopt different algorithm, the data
reliability is very high. Even two HDDs are broken
at the same time, there is no data loss risk.
Comparing to RAID5, the RAID6 needs to allocate
larger HDD space for odd/even verification
information, so its read/write is even worse.
4