Raid and its levels

Raid and its levels

• 1.
  RAID and ItsLevels Presented By: Hassan Mehmood 2419 Semester: 7th(BS.IT)
• 2.
  Define: Raid stands forRedundant array of inexpensive/ independent disks. “It is a data storage virtualization technology that combines multiple disk drive components into a logical unit for the purposes of performance improvement.” Raid Levels: 1. Raid 0 2. Raid 1 3. Raid 2 4. Raid 3 5. Raid 4 6. Raid 5 7. Raid 6 What is RAID
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  Why we needRaid  Computing speeds double every 3 years  Disk speeds can’t keep up  I/O Performance and Availability Issues! Raid allows us to avoid those issues by, 1.Parallelism 2.Load Balancing 3.Redundancy: Mirroring, or Striping with Parity 4.Availability/Cost
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  Mirroring  Keep tocopies of data on two separate disks  Gives good error recovery if some data is lost, get it from the other source  Expensive requires twice as many disks  Write performance can be slow have to write data to two different spots  Read performance is enhanced can read data from file in parallel Same data written to both disks.
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  Striping  Take filedata and map it to different disks  Allows for reading data in parallel file data block 1block 0 block 2 block 3 Disk 0 Disk 1 Disk 2 Disk 3
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  Raid 0: It splitsdata evenly across two Or more disks. RAID 0 is normally used to increase performance, although it can also be used as a way to create a large logical disk out of two or more physical ones. RAID Levels
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  RAID Levels  Raid1: It creates an exact copy or mirror of set of data on two disks. This is useful when read performance is more important than data storage capacity. Write through-put is always slower because every drive must be updated on each entry.
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   Raid 2: ItStripes data at bit level and uses hamming code for error correction. All disks participate in the execution of every I/O. The spindles of individual disks are synchronized so that each disk head is in the same position on each disk at any time. RAID 2 is seldom deployed because costs to implement are usually prohibitive and gives poor performance with some disk I/O operations. RAID Levels
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   Raid 3: Itstripes data at byte-level with dedicated parity bit. All disks are synchronized such that each bit is on different drive. Raid 3 is not commonly used. All disks can accessed in Parallel. RAID Levels
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   Raid 4: Itstripes data at block-level with dedicated parity bit. It is very rarely used in practice. Net App is the enterprise that previously used this Raid. This approach allows multiple writes to be done but that makes performance slower. RAID Levels
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   Raid 5: Itstripes data at block-level with distributed parity. Parity information is distributed among the drives. Upon failure of a single drive , subsequent reads can be calculated so no data is lost. It requires at least three disks. RAID Levels
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   Raid 6: Itstripes data at block-level with double distributed parity. Double parity provides fault tolerance upto two drives. Performance varies depending on how it is implemented. RAID Levels
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  Feature R-0 R-1R-2 R-3 R-4 R-5 R-6 Minimum drives 2 2 3 3 3 3 4 Fault Tolerance 0 N-1 1 1 1 1 2 Read Performance High High High High High High High Write Performance High Medium Medium Low Low Low Low Capacity Utilization 100% 50% 50% 67- 94% 50- 88% 50- 88% 50- 88% Best Raid Level???
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  Thank You!