Basics about RAID
RAID
This is a quick premiere about the RAID(Redundant array of inexpensive disks). The knowledge is quite useful if you ever
have to choose some hardware for hosting critical applications.
General RAID Concepts.
Mirroring - Same data is written to two different disks using the same
controller.
Duplexing - Same data written to two different disks using differnt controllers.
Striping - Chopping up a single file among different disks to improve the read access time as different disks can be accessed parallely improving performance. Doesnt add any redundancy to the data so doesnt improve data protection.
Parity - Take N pieces of the data calculate N + 1 piece by XORing the data. If one of the N + 1 pieces are missing we can find that using the rest N. This is the general concept of parity because of XOR.
Advantages - doesnt waste 50% storage (N-1/N where N is the total number of disks in the array is the storage efficiency). Disadvantages - lots of computation use hardware controller.
RAID 0 - Striping without parity - No data redundancy - So no
way to restore if disk failed - Good Read / Write speeds.
RAID 1 - Mirroring - High Overhead cost because only 50% of the
storage is used and the other 50% is duplicate data - No performance improvement like striping - Write slower as has to write
the duplicate copy - read is improved
RAID 2 - Bit-level striping with Hamming code ECC
Read Fair / Write Poor.
RAID 3 - Byte-level striping with dedicated parity.
Read Good / Write Poor.
RAID 4 - Block-level striping with dedicated parity
Read Very Good / Write poor.
RAID 5 - Block-level striping with distributed parity.
Read Very Good / Write Fair
RAID 6 - Block-level striping with dual distributed parity.
Read Very Good/ Write Poor Can tolerate failure of two disks
in the array due to redundant second parity.
RAID 0+1/ 1+0 - Stripping with Mirroring/ Mirroring with Stripping
This is a quick premiere about the RAID(Redundant array of inexpensive disks). The knowledge is quite useful if you ever
have to choose some hardware for hosting critical applications.
General RAID Concepts.
Mirroring - Same data is written to two different disks using the same
controller.
Duplexing - Same data written to two different disks using differnt controllers.
Striping - Chopping up a single file among different disks to improve the read access time as different disks can be accessed parallely improving performance. Doesnt add any redundancy to the data so doesnt improve data protection.
Parity - Take N pieces of the data calculate N + 1 piece by XORing the data. If one of the N + 1 pieces are missing we can find that using the rest N. This is the general concept of parity because of XOR.
Advantages - doesnt waste 50% storage (N-1/N where N is the total number of disks in the array is the storage efficiency). Disadvantages - lots of computation use hardware controller.
RAID 0 - Striping without parity - No data redundancy - So no
way to restore if disk failed - Good Read / Write speeds.
RAID 1 - Mirroring - High Overhead cost because only 50% of the
storage is used and the other 50% is duplicate data - No performance improvement like striping - Write slower as has to write
the duplicate copy - read is improved
RAID 2 - Bit-level striping with Hamming code ECC
Read Fair / Write Poor.
RAID 3 - Byte-level striping with dedicated parity.
Read Good / Write Poor.
RAID 4 - Block-level striping with dedicated parity
Read Very Good / Write poor.
RAID 5 - Block-level striping with distributed parity.
Read Very Good / Write Fair
RAID 6 - Block-level striping with dual distributed parity.
Read Very Good/ Write Poor Can tolerate failure of two disks
in the array due to redundant second parity.
RAID 0+1/ 1+0 - Stripping with Mirroring/ Mirroring with Stripping
posted by Suresh at
7:20 AM
