Thecus N4310 Series, Руководство пользователя

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123 Appendix B: RAID Basics
line customer service. Use it also for applications with high read requests but low write requests.
RAID 5 includes disk striping at the byte level and parity information is written to several hard disk
drives. If a hard disk fails the system uses parity stored on each of the other hard disks to recreate all
missing information.
RAID 6
RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using
a second independent distributed parity scheme (dual parity)
Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is
calculated and written across all the drives; RAID 6 provides for an extremely high data fault toler-
ance and can sustain two simultaneous drive failures.
This is a perfect solution for mission critical applications.
RAID 10
RAID 10 is implemented as a striped array whose segments are RAID 1 arrays. RAID 10 has the same
fault tolerance as RAID level 1.
RAID 10 has the same overhead for fault-tolerance as mirroring alone. High I/O rates are achieved by
striping RAID 1 segments.
Under certain circumstances, RAID 10 array can sustain up to 2 simultaneous drive failures
Excellent solution for applications that would have otherwise gone with RAID 1 but need an addi-
tional performance boost.
JBOD
Although a concatenation of disks (also called JBOD, or “Just a Bunch of Disks”) is not one of the num-
bered RAID levels, it is a popular method for combining multiple physical disk drives into a single
virtual one. As the name implies, disks are merely concatenated together, end to beginning, so they
appear to be a single large disk.
As the data on JBOD is not protected, one drive failure could result total data loss.
Stripe Size
The length of the data segments being written across multiple hard disks. Data is written in stripes
across the multiple hard disks of a RAID. Since multiple disks are accessed at the same time, disk strip-
ing enhances performance. The stripes can vary in size.
Disk Usage
When all disks are of the same size, and used in RAID, Thecus IP storage disk usage percentage is
listed below:
RAID Level Percentage Used
RAID 0 100%
RAID 1 1/n x 100%
RAID 5 (n-1)/n x 100%
RAID 6 (n-2)/n x 100%
RAID 10 50%
JBOD 100%
n: HDD number