HP LH4r Installation and configuration of the HP NetRAID, NetRAID-1 and NetRAI - Page 25

Non-spanned Arrays with Redundancy: RAID Levels 1, 3, and 5

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Chapter 2 RAID Overview Non-spanned Arrays with Redundancy: RAID Levels 1, 3, and 5 RAID 1: Mirroring In RAID 1 configurations, data on one disk is completely duplicated on another disk. This is called mirroring. RAID 1 must be configured on a two-disk array. (The array cannot contain more than two disk drives.) With this algorithm, if either of the two disks fail, data is available from the duplicate disk. Data is written as follows: Stripe 1 Stripe 2 Stripe 3 Disk 1 Block 1 Block 2 Block 3 Disk 2 Block 1 Block 2 Block 3 RAID 1 Advantages There is no data loss or system interruption due to disk failure, because if one disk fails, the other is available. Read performance is fast, because data is available from either disk. RAID 1 Disadvantages Costs are high, because 50% of all disk space is allocated for data protection. Actual data capacity is only 50% of physical capacity. RAID 1 Summary Choose RAID 1 if high availability and performance are important, but cost is not a major concern. 17

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Chapter 2
RAID Overview
17
Non-spanned Arrays with Redundancy: RAID Levels 1, 3, and 5
RAID 1: Mirroring
In RAID 1 configurations, data on one disk is completely duplicated on another
disk. This is called
mirroring
. RAID 1 must be configured on a two-disk array.
(The array cannot contain more than two disk drives.) With this algorithm, if
either of the two disks fail, data is available from the duplicate disk. Data is
written as follows:
Disk 1
Disk 2
Stripe 1
Block 1
Block 1
Stripe 2
Block 2
Block 2
Stripe 3
Block 3
Block 3
RAID 1 Advantages
There is no data loss or system interruption due to disk failure, because if one
disk fails, the other is available.
Read performance is fast, because data is available from either disk.
RAID 1 Disadvantages
Costs are high, because 50% of all disk space is allocated for data protection.
Actual data capacity is only 50% of physical capacity.
RAID 1 Summary
Choose RAID 1 if high availability and performance are important, but cost is
not a major concern.