What is RAID History> It first defined by David A. Patterson, Garth A. Gibson, and Randy Katz at the University of California, Berkeley in 1987 to describe a redundant array of inexpensive disks.> What is RAID - It is a technology that allowed computer users to achieve high levels of storage reliability from low-cost and RAID allows you to store the same data redundantly (in multiple paces) in a balanced any to improve overall performance.
Benefits of RAID> Data loss can be very dangerous for an organization> RAID technology prevents data loss due to disk failure> RAID technology can be implemented in hardware or software> Servers make use of RAID technology
Hardware vs. Software RAID> Software RAID • Software RAID: run on the server’s CPU • Directly dependent on server CPU performance and load • Occupies host system memory and CPU operation, degrading server performance> Hardware RAID • Hardware RAID: run on the RAID controller’s CPU • Does not occupy any host system memory. Is not operating system dependent • Host CPU can execute applications while the array adapters processor simultaneously executes array functions: true hardware multi-tasking
RAID • Redundant Arrays of Independent Drives • Benefits – Improved data availability – Improved I/O performance – Increased scalability • Levels supported by Array controllers – RAID 0 – Data striping – RAID 1 – Drive mirroring – RAID 4 – Data guarding – RAID 5 – Distributed data guarding – RAID 6/ADG - Advanced data guarding – RAID 0+ 1 – Mirroring and striping
Single Drive and Drive Arrays Single Drive Drive Arrays
Drive Array Features • Data striping across multiple drives • Multiple channels • Request processing Single Fixed Disk Drive Drive 1 Array 3 2 4 1 2 3 4 1234 Drive Array Organization
RAID Level 0 — Data Striping File divided into chunks (or segments) and then written (striped) across multiple drives
RAID 0 Uses striping I/O performance gain No Data redundancy Not fault tolerant Not considered “true” RAID
Striping Factor 64KB Host Data Fixed Striping Factor Based on Drive Sizes
RAID Level 1 — Drive Mirroring Data Written to Two or More Separate Mirrored Drives
RAID 1Uses mirroring Also known as duplexingFault tolerantHigh Disk overhead Mirroring typically handled system softwareSimplest RAID design
RAID Level 0+1 Disk 0 is mirrored to disk 2 and disk 1 is mirrored to disk 3. Then disk 0 is striped with disk 1 and disk 2 is striped to disk 3.
RAID 0+1 RAID 1+0 requires an array with four or more physical disks. The disks are mirrored in pairs and data blocks are striped across the mirrored pairs Advantages Highest read and write performance No loss of data as long as no failed disks are mirrored to any other failed disk Disadvantages Expensive and Low disk capacity
RAID Level 4 — Data Guarding Data striped across multiple drives and then its parity sum is calculated and written to a dedicated parity drive
RAID 4 Advantages: Disadvantages: Very high read rates Very slow write rates Even small writes fill up Multiple files read at parity write queue once Inefficient data recovery Uses: Even more Complex Web Servers, and Controller Design than other high read, low RAID 3 write situations
RAID Level 5 — Distributed Data GuardingData is striped across multiple drives and then its parity sumcalculated and striped across multiple drives. Example of 64KBstriped across five drives using 4KB chunks.
RAID 5 RAID 5 uses a parity data formula to create fault tolerance. In RAID 5 each block of data stripe contains parity data that is calculated for the other data blocks in that strip. The blocks of parity data are distributed over the physical disks that make up the logical drive with each physical disk containing only one block of parity data It is referred to as data guarding. Advantages High read performance No loss of data if one physical disk fails More usable disk capacity Disadvantages Relatively low write performance Data loss occurs if a second disk fails before data from the first failed disk is rebuilt
RAID ADG (Advanced Data Guarding)> RAID ADG is similar to RAID 5 except this RAID level writes 2 sets of parity stripped across all drives.> Protects against failure of ANY 2 drives in the array A B C P Q D E P Q F G P Q H I P Q J K L RAID ADG
RAID ADG (Advanced Data Guarding)> P = f1(A, B, C) = RAID 5 Parity> Q = f2(A, B, C) = new ADG Parity A B C P Q D E P Q F G P Q H I P Q J K L RAID ADG
RAID ADG (Advanced Data Guarding)> If 2 parity drives are selected, the system can sustain failure of ANY 2 drives. X X A B C P Q D E P Q F G P Q H I P Q J K L RAID ADG
RAID ADG (Advanced Data Guarding) orRAID 6 RAID advanced data guarding sometimes referred to as RAID 6, is similar to RAID 5 in that parity data is generated and stored to protect against data loss caused by physical disk failure Advantages High read performance High data availability More usable disk capacity
RAID 10 Combining RAID 0 and RAID 1 is often referred to as RAID 10 which offers higher performance than RAID 1 but at much higher cost Uses multiple (mirrored) RAID 1 in a single array Data striped across all mirrored sets Very high fault tolerance High performance rate
RAID 10Characterized by: Each drive duplicated High implementation cost
Comparing RAID Levels RAID 0 RAID 1 RAID 5 RAID 10Read High 2X High HighWrite High 1X Medium HighFault No Yes Yes YestoleranceDisk High Low High LowutilizationKey Data lost Use double the Lower throughput Very expensive, notproblems when any disk disk space with disk failure scalable failsKey High I/O Very high I/O A good overall High reliability withadvantages performance performance balance good performance
On-Line Spare • Replacement for failed drive • Requires hardware fault tolerance • Background rebuild process • Four On-Line Spares maximum (Smart Array controller) Mirrored Mirrored Pair Pair Mirrored Pair On-Line On-Line Spare Spare Before During After Failure Failure Replacement
Conclusion So what have we learned here? Well we have learned that RAID is not just a bug spray. RAID is a good solution for companies or individuals carving more transfer performance, redundancy and storage capacity in their data storage systems.