RAID

What is RAID? RAID (Redundant Array of Independent Disks ) is a way of storing the same data in different places on multiple hard disks to protect data in case of a drive failure.

Types of RAID ?Two types of RAID is there Software & Hardware. Software RAID –Intel Rapid Storage Technology, LsiMega Raid Storage Manager. Hardware RAID --1) Integrated (Lsi, Intel ). 2) Add-on hwraid card (Adaptec, Lsi, Super micro, Broadcom ).

What is DiskStriping? Disk striping is the process of dividing a body of data into blocks and spreading the data blocks across multiple storage devices, such as hard disk or solid-state drives (SSDs). What is distributed parity? Distributed parity is nothing but a Redundant information (parity) which is alternately stored on all disks. When a disk fails, the virtual disk still works. The data is reconstructed from the surviving disks and the parity alternately stored on the disks.

Reference: RAID Levels

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RAID 0 –Integrated Striping (IS)

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RAID 1 –Integrated Mirroring (IM)

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RAID 5 –Striping with Distributed Parity

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RAID 10, 1E –Integrated Mirroring Enhanced (IME)

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RAID 6 –Striping with Dual Distributed Parity

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RAID 50 –RAID 5 + 0

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RAID 60 –RAID 6 + 0

RAID 0: Integrated Striping (IS)

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Block-level striping without parity or mirroring

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Minimum of 2 disks required

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Logical volume’s capacity is equal to the sum of the drive capacities

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Excellent performance

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No fault tolerance and no redundancy

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If a disk fails, data is lost

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Data is transferred to and from disks simultaneously

Main Advantage: SPEED

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Block-level mirroring without striping or parity

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Maximum of 2 disks

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Logical volume’s capacity is equal to half the total drive capacity

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Write performance slightly slower than a single drive because data must be written to both disks

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Read performance is improved because data is transferred from multiple disks at once

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Excellent redundancy –always a mirrored copy

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If a disk fails, data is still available

RAID 5: Striping with Parity

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Block-level striping with distributed parity

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Minimum of 3 disks required

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Logical volume’s capacity is equal to the total drive capacity n-1

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Read performance is good due to striping

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Write performance is slower than RAID 0 because parity must be generated

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Good redundancy –Up to one drive can fail

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Supports dedicated hot-spare

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[Note –If RAID 5 is down, we can’t access data separately by connecting one HDD. ]

What is HOT Spare?

When one of the hard drives in a RAID group fails and an idle or standby drive immediately replaces the failed hard drive, this drive is known as a “hot spare”.The “hot spare” hard drive doesn't store any data when it's idle.

Types of HOT Spare?

Dedicated Hot Spare –It’s for dedicated RAID Group Configuration.

Global Hot Spare –It’s support multiple RAID groups with in WS / Server / SAN / NAS / blade / cluster some extend in cloud also.

RAID 10: Integrated Mirroring Enhanced (IME)

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Block-level mirroring & block-level striping

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Also known as RAID 1 + 0

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Minimum of 4 disks required

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Logical volume’s capacity is equal to half the total drive capacity

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Excellent performance because blocks are striped as in RAID 0

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Excellent redundancy because blocks are mirrored as in RAID 1

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Up to 2 disks can fail as long as they are not part of the same mirrored set