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RAID 10
RAID 1+0 sometimes called RAID 1&0, or RAID 10, is similar to a RAID 0+1 with exception that the RAID levels
used are reversed — RAID 10 is a stripe of mirrors. Below is an example where three collections of 120 GB
level 1 arrays are striped together to make 360 GB of total storage space.
All but one drive from each RAID 1 set could fail without damaging the data. However, if the failed drive is not
replaced, the single working hard drive in the set then becomes a single point of failure for the entire array. If that
single hard drive then fails, all data stored in the entire array is lost. As is the case with RAID 0+1, if a failed drive
is not replaced in a RAID 10 configuration then a single uncorrectable media error occurring on the mirrored hard drive
would result in data loss. Some RAID 10 vendors address this problem by supporting a "hot spare" drive, which automatically
replaces and rebuilds a failed drive in the array.
Given these increasing risks with RAID 10, many business and mission critical enterprise environments are beginning to
evaluate more fault tolerant RAID setups that add underlying disk parity. Among the most promising are hybrid approaches
such as RAID 51 (mirroring above single parity) or RAID 61 (mirroring above dual parity). RAID 10 is often the primary choice
for high-load databases, because the lack of parity to calculate gives it faster write speeds.
RAID 10 Capacity: (Size of Smallest Drive) * (Number of Drives) / 2
The Linux kernel RAID10 implementation (from version 2.6.9 and onwards) is not nested. The mirroring and striping is
done in one process. Only certain layouts are standard RAID 10 with the rest being proprietary.
RAID 0+1
RAID 0+1 (also called RAID 01, not to be confused with RAID 1), is a RAID used
for both replicating and sharing data among disks. The difference between RAID
0+1 and RAID 1+0 is the location of each RAID system — RAID 0+1 is a mirror of
stripes. The size of a RAID 0+1 array can be calculated as follows where n is
the number of drives (must be even) and c is the capacity of the smallest drive
in the array:
Size = (n x c) ÷ 2
Consider an example of RAID 0+1: six 120 GB drives need to be set up on a RAID
0+1. Below is an example where two 360 GB level 0 arrays are mirrored, creating
360 GB of total storage space.
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