1. Redundant Array of Independent Disks Borislav Varadinov Telerik Software Academy academy.telerik.com System Administrator Marian Marinov CEO of 1H Ltd. mm@1h.com bobi@itp.bg

2.  What is RAID?  How RAID provides fault tolerance?  How the parity is calculated?  RAID Levels  What is a hot spare disk?  When planning RAID levels, consider?  RAID implementation options? 2

3. RAID can provide fault tolerance RAID can provide fault tolerance RAID can provide performance benefits by spreading disk I\O across multiple disks RAID can provide performance benefits by spreading disk I\O across multiple disks RAID can be configured using several different levels (configurations) RAID can be configured using several different levels (configurations) RAID cannot replace the backup! RAID cannot replace the backup! 3 Redundant array of independent disks or RAID combines multiple disks into a single logical unit to provide fault tolerance and performance

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6.  RAID can provide fault tolerance by using  Disk mirroring  Parity information  The parity information is based on the standard logical operation exclusive or (XOR) 6 XYXOR 000 101 011 110

7. 7 1 0 1 0 1 1 1 1 1 1 0 0 1 0 0 1 0 0 1 0 1  Demonstration Block 1 Block 2 Parity

8.  A non-redundant disk array  Very good performance for read and write  Storage efficiency: 100 %  Minimum disk == 2 8 Failure of any drive results in loss of all data. RAID 0 is not recommended for critical data. Failure of any drive results in loss of all data. RAID 0 is not recommended for critical data. A5 A6 A4 A3 A2 A1 Disk 1 Disk 2

9.  The data is duplicated on two separate disks  Storage efficiency: 50 %  Disks == 2 9 A3 A2 A1 Disk 1 Disk 2

10.  Minimum disk == 3  Storage efficiency: Number of Drives - 1 10 C1 Cp B2 B1 A2 A1 Disk 1 Disk 2 C2 C3 B3 Bp Ap A3 Disk 3 Disk 4 Dp D1 D2 D3

11.  Storage efficiency: Number of Drives – 2  Minimum disk == 4 11 C1 Cp B2 B1 A2 A1 Disk 1 Disk 2 Cq C3 Bq Bp Ap A3 Disk 3 Disk 4 Dp Dq D2 D3 C3 B3 Aq Disk 5 D3

12.  Mirror of stripes  Storage efficiency: 50 %  Minimum disk == 4 12 A5 A3 A1 A7 A6 A4 A2 A8 A5 A3 A1 A7 A6 A4 A2 A8 RAID 0 RAID 1

13.  Stripe of mirrors  Storage efficiency: 50 %  Minimum disk == 4 13 A5 A3 A1 A7 A5 A3 A1 A7 A6 A4 A2 A8 A6 A4 A2 A8 RAID 1 RAID 0

14. 14 A7 A4 A1 A7 A4 A1 RAID 1 RAID 0 A8 A5 A2 A8 A5 A2 RAID 1 A9 A6 A3 A9 A6 A3 RAID 1 A7 A4 A1 A8 A5 A2 RAID 0 RAID 1 A8 A5 A2 A9 A6 A3 RAID 0 A9 A6 A3 A7 A4 A1

15. 15 Hot spare is an extra disk drive in a RAID configuration that is ready and waiting to be put into action automatically when another drive fails A3 A2 A1 Disk 1 Disk 2 Hot Spare Mirror RAID1 Mirror RAID1

16.  Hardware RAID  Software RAID 16

17.  Cost  Level of redundancy  Performance  Storage utilization  Type of disks  Count of disks  RAID Controller 17

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