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RAID

RAID. Rithy Chhay Shari Holstege CMSC 691X: UNIX Systems Administration. What is RAID?. Redundant Array of Inexpensive/Independent Disks RAID can improve availability and throughput (although actually reliability – whether anything is broken – suffers because of the larger number of disks)

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RAID

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  1. RAID Rithy Chhay Shari Holstege CMSC 691X: UNIX Systems Administration

  2. What is RAID? • Redundant Array of Inexpensive/Independent Disks • RAID can improve availability and throughput (although actually reliability – whether anything is broken – suffers because of the larger number of disks) • Data is stored on several disks instead of a single disk

  3. RAID Levels

  4. RAID 0: Striping • This level offers no redundancy – no extra data is kept. • The performance is the best of any level. Throughput is increased by striping data across several disks.

  5. RAID 1: Mirroring • Uses twice as many disks • Whenever data is written to one disk, that data is also written to a redundant disk so that there are always two copies of the information • When a disk fails, the system merely goes to its mirror for the data

  6. RAID 3: Bit-Interleaved Parity • Reads and writes go to all disks in a group, with one extra disk to hold the check information in case there is a failure. • Parity is simply the sum of the data in all the disks modulo 2. Lost data can be reconstructed by examining the parity. • Every access goes to all disks.

  7. RAID 4: Block-Interleaved Parity • Allows applications to do smaller accesses than RAID 3, allowing independent accesses to occur in parallel. • Small, independent reads are easy – simply read the data and then check for error detection. • Writes are harder – old data is read, new data is compared, and only those parity bits whose values change are updated. • The parity disk becomes a bottleneck, since the parity disk must be updated on every write.

  8. RAID 5: Block-Interleaved Distributed Parity • This is a way to get rid of the bottleneck of RAID 4 – distribute the parity information across all disks. 0 1 2 P0 0 1 2 P0 3 4 5 P1 3 4 P1 5 6 7 8 P2 6 P2 7 8 9 10 11 P3 P3 9 10 11 RAID 4 RAID 5

  9. Higher Levels • RAID 6: Adds a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance • RAID 7: Includes a real-time embedded operating system as a controller, caching via a high-speed bus, and other characteristics of a stand-alone computer.

  10. Higher Levels (cont.) • RAID 10: Offers an array of stripes in which each stripe is a RAID-1 array of drives. This offers higher performance than RAID-1 but at much higher cost. • RAID 53: Offers an array of stripes in which each stripe is a RAID 3 array of disks. This offers higher performance than RAID 3 but at much higher cost.

  11. RAID in Linux • Linux offers built-in software RAID capabilities • Advantages of Linux Software RAID • Threaded rebuild process • Fully kernel-based configuration • Backgrounded array reconstruction • Hot-swappable drive support • Automatic CPU detection to use CPU Optimizations

  12. Options for Software RAID • You can create a software RAID in Linux using only one hard disk! • You can create a software RAID in Linux using multiple drives. • Specifying the type of RAID you wish to install on your systems, depends on how they are used; refer back to RAID Levels.

  13. Creating RAID Partitions • Using Disk Druid, Select software RAID from the Filesystem Type • Select the drive on which the RAID is to be created • Enter the size of the RAID partition • Choose other options as needed for your RAID

  14. Software RAID Configuration • Once RAID partitions have been created, select the Make RAID option on the Disk Druid main partitioning screen. • Enter a mount point, select a filesystem, and choose your RAID Level. • A spare partition can be specified for RAID 1 and RAID 5

  15. RAID Drive Summary • You have now created a software RAID in Linux. • Try it at home!

  16. Rules of Thumb • When setting up a RAID with different sized hard drives, configure partitions on each drive to be the same size. • Whenever possible, use the same hardware specifications for multiple hard drives • Creating a software RAID on a single hard drive will slow performance because data must be written twice using only one head.

  17. Do-It-At-Home RAID • Build your own home RAID using • Soyo KT-SY333 Dragon Ultra Motherboard • AMD Athlon XP 2200+ CPU • 1024MB DDR PC2700 RAM • (4) 160GB Maxtor DiamondMax DX540 Hard drives • Multiple cooling fans • Large Tower Case with a 400W power supply

  18. Soyo KT-SY333 Motherboard • Embedded Hipoint IDE-RAID chip, providing ATA-133 IDE-RAID 0,1,0+1 • Setup both Hardware and Software RAIDs simultaneously!

  19. Setting up your RAID • Enter the BIOS set-up of your Soyo motherboard. • Enable the desired hardware RAID Level. • Install Linux on your machine with or without the software RAID option. • Selecting hardware RAID Level 0 and software RAID Level 0 will provide the best level of performance. • This setup provides for a fast 640GB RAID.

  20. Additional Resources • Patterson, David A. and John L. Hennessy. Computer Architecture: A Quantitative Approach. San Francisco, CA: Morgan Kaufmann Publishers, Inc., 1996. • http://whatis.techtarget.com/definition/0,289893,sid9_gci214332,00.html

  21. Additional Resources … • http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/custom-guide/ • http://www.soyotek.com/products/proddesc.php?id=46 • http://www.maxtor.com/ • http://www.amd.com/

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