RAIDRAID Rithy Chhay Shari Holstege CMSC 691X: UNIX Systems Administration.
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Transcript of RAIDRAID Rithy Chhay Shari Holstege CMSC 691X: UNIX Systems Administration.
RAIDRAIDRAIDRAIDRithy ChhayRithy Chhay
Shari HolstegeShari Holstege
CMSC 691X: UNIX Systems CMSC 691X: UNIX Systems AdministrationAdministration
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
RAID Levels
RAID LevelFailures Survived
Data Disks
Check Disks
0 Nonredundant 0 8 0
1 Mirrored 1 8 8
2 Memory-style ECC 1 8 4
3 Bit-interleaved parity 1 8 1
4 Block-interleaved parity 1 8 1
5 Block-interleaved distributed parity
1 8 1
6 P+Q redundancy 2 8 2
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.
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
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.
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.
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
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P0
P1
P2
P3
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P3
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P2
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P1
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P0
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RAID 4 RAID 5
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.
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.
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
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.
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
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
RAID Drive Summary
• You have now created a software RAID in Linux.
• Try it at home!
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.
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
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!
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.
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
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/