Promise Technology ultratrak RM8000, Руководство пользователя

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UltraTrak SX4000, SX8000 & RM8000 User Manual
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RAID 3: Block Striping with Parity Drive
RAID level 3 organizes data across the physical drives of the array, and stores
parity information on to a drive dedicated to this purpose. This organization
allows increased performance by accessing multiple drives simultaneously for
each operation, as well as fault tolerance by providing parity data. In the event of
a hard drive failure, data can be re-calculated by the RAID system based on the
remaining drive data and the parity information.
The adjustable block size of the RAID 3 array allows for performance tuning
based on the typical I/O request sizes for your system. The block size must be
set at the time it is created and cannot be adjusted dynamically. Generally, RAID
Level 3 tends to exhibit lower random write performance due to the heavy
workload going to the dedicated parity drive for parity recalculation for each I/O.
The capacity of a RAID 3 array is the smallest drive size multiplied by the number
of drives less one. Hence, a RAID 3 array with (4) 100 GB hard drives will have a
capacity of 300GB. An array with (2) 120GB hard drives and (1) 100GB hard
drive will have a capacity of 200GB.
Data Drives Parity Drive
1 parity
2 parity
3 parity
4 parity
1d
2d
3d
4d
1c
2c
3c
4c
1b
2b
3b
4b
1a
2a
3a
4a
Data Stripes
Figure 19. RAID 3 Multiple Drives Stripe Data w/ One Dedicated Parity Drive