Bull NovaScale T840, User Manual

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User Guide
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RAID Levels
RAID 0 and RAID 1
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RAID0 (striping)
When a logical drive is striped, the read and write blocks of data are interleaved
between the sectors of multiple disk drives. Performance is increased, since the
workload is balanced between drives or “members” that form the logical drive.
Identical drives are recommended for performance as well as data storage
efficiency. The logical drive's data capacity is equal to the number of drive
members multiplied by the smallest logical drive member's capacity.
RAID 0 Stripe interleaves data across multiple drives For example, one 100GB
and three 120GB drives will form a 400GB (4 x 100GB) logical drive instead of
460 GB.
Warning
■
RAID0 does not have data redundancy. When a hard disk
drive failure occurs, data cannot be restored.
■
Logical capacity of the array becomes a multiple of the con-
nected hard disk drive.
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RAID1 (mirroring)
When a logical drive is mirrored, identical data is written to a pair of disk drives,
while reads are performed in parallel. The reads are performed using elevator seek
and load balancing techniques where the workload is distributed in the most
efficient manner. Whichever drive is not busy and is positioned closer to the data
will be accessed first.
With RAID 1, if one disk drive fails or has errors, the other mirrored disk drive
continues to function. This is called Fault Tolerance. Moreover, if a spare disk
drive is present, the spare drive will be used as the replacement drive and data will
begin to be mirrored to it from the remaining good drive.
Due to the data redundancy of mirroring, the capacity of the logical drive is only
the size of the smallest disk drive. For example, two 100GB disk drives which
have a combined capacity of 200GB instead would have 100GB of usable storage
RAID Configuration Number of required hard disk drives
RAID 0 2
RAID 1 2
RAID 10 4
RAID 5 3