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What is RAID10?
Posted by James Huang on 21 January 2013 17:23
RAID10 is a stripe(RAID0) of mirrors(RAID1) and least take four hard disks.

RAID0 uses striping to write data across multiple drives simultaneously. This means that when you write a 5GB file across 5 drives, 1GB of data is written to each drive. Parallel reading of data from multiple drives can have a significant positive impact on performance. RAID0 has good performance but if one of those drives fail, all of your data will be lost.

RAID1 uses mirroring to write data to multiple drives. This means that when you write a file, the file is actually written to multiple disks. If one of the disks fails, you simply replace it and rebuild the mirror. With RAID1, you must purchase double the amount of storage space that your data requires.

When you create RAID10, all the hard disks is divided into several sets of RAID 1, disk#1 & #2 are created a set of RAID 1, disk#3 & #4 are created another RAID1, disk#5 & #6 are created as another RAID1... then these all sets of  RAID1 will be combined into a RAID0. The total storage capacity of RAID10 is the sum of two sets of RAID1's storage capacity.

RAID 10 combines the performance of RAID0 with the redundancy of RAID 1. RAID 10 can survive the loss of one disk from each sets of RAID1 but can't survive the loss of two disks in the same set of RAID1, and it could use difference size of HDDs.

Here is an example for your reference,

4 hard disks to create the RAID10

Disk#1 4TB
Disk#2 4TB
Disk#3 2TB
Disk#4 2TB

Disk 1 & 2 will be created a set of RAID 1(storage capacity:4TB)
Disk 3 & 4 will be created another set of RAID 1(storage capacity:2TB)

RAID 10's total storage capacity is 6TB (the sum of two sets of RAID 1's storage capacity). In case four drives are in use initially a pair of drives is mirrored as in RAID 1 and further striped as in RAID 0.

Another example,

Disk#1 4TB
Disk#2 2TB
Disk#3 4TB
Disk#4 2TB

Disk 1 & 2 will be created a set of RAID 1(storage capacity:2TB)
Disk 3 & 4 will be created another set of RAID 1(storage capacity:2TB)

RAID 10's total storage capacity is 4TB.

Compare to RAID6, RAID10 could allow lost maxinum N/2 disks lost in a N-disks system, once RAID10 lost two disks in the same RAID1 set, the whole RAID10 will be corrupted. RAID6 could allow lost 2 any disks.
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