Raid(Storage Technology)
- 1. RAID -REDUNDANT ARRAY OF INDEPENDENT DISK By R.VANITHA SHREE SKCET
- 2. RAID-intro RAID is an enabling technology that leverages multiple disks as part of a set, which provides data protection against HDD failures. In general, RAID implementations also improve the I/O performance of storage systems by storing data across multiple HDDs. “ Redundant Arrays of Inexpensive Disks” The term RAID has been redefined to refer to independent disks, to reflect advances in storage technology.
- 3. Implementation of RAID-two types; hardware and software Software RAID Software RAID uses host-based software to provide RAID functions. It is implemented at the operating-system level and does not use a dedicated hardware controller to manage the RAID array. Software RAID affects overall system performance Software RAID does not support all RAID levels. Since it is implemented at the OS level,the RAID should be OS compatible
- 4. HARWARE RAID The specialized RAID controller is installed in the host and HDDs are connected to it. The RAID Controller interacts with the hard disks using a PCI bus. Manufacturers also integrate RAID controllers on motherboards. This integration reduces the overall cost of the system, but does not provide the flexibility required for high-end storage systems. Key functions of RAID controllers are: Management and control of disk aggregations Translation of I/O requests between logical disks and physical disks Data regeneration in the event of disk failures.
- 5. RAID COMPONENTS HDDs inside a RAID array are usually contained in smaller sub-enclosures. These sub-enclosures, or physical arrays, hold a fixed number of HDDs. A subset of disks within a RAID array can be grouped to form logical associations called logical arrays(or)RAID set The number of HDDs In a logical array depends on the RAID level used.
- 6. Raid levels are defined on the basis of striping , mirroring and parity. These techniques determine the data availability and performance characteristics of an array STRIPING A RAID set is a group of disks. Within each disk, a predefined number of contiguously addressable disk blocks are defined as strips. The set of aligned strips that spans across all the disks within the RAID set is called a stripe. All strips in a stripe have the same number of blocks, and decreasing strip size means that data is broken into smaller pieces when spread across the disks. Strip size (also called stripe depth) describes the number of blocks in a strip,. Stripe width refers to the number of data strips in a stripe. striping may significantly improve I/O performance , no protection of data
- 7. MIRRORING Mirroring is a technique whereby data is stored on two different HDDs, yielding two copies of data. In the event of one HDD failure, the data is intact on the surviving HDD. In addition to providing complete data redundancy, mirroring enables faster recovery from disk failure. MIRRORING provides only protection of data, the amount of storage capacity needed is twice the amount of data being stored. Therefore, mirroring is considered expensive and is preferred for mission- critical applications that cannot afford data loss. Read operation can be done, but write requires time to write in both the disks
- 8. PARITY Parity is a method of protecting striped data from HDD failure without the cost of mirroring. An additional HDD is added to the stripe width to hold parity, Parity is a redundancy check that ensures full protection of data without maintaining a full set of duplicate data. Parity information can be stored on separate, dedicated HDDs or distributed across all the drives in a RAID set. Parity requires 25 percent extra disk space compared to mirroring requiring 100 percent extra disk space. Parity is recalculated every time there is a change in data. This recalculation is time-consuming and affects the performance of the RAID controller.
- 9. RAID 0 In a RAID 0 configuration, data is striped across the HDDs in a RAID set. It utilizes the full storage capacity by distributing strips of data over multiple HDDs in a RAID set. When the number of drives in the array increases, performance improves because more data can be read or written simultaneously. RAID 0 is used in applications that need high I/O throughput. However it does not provide data protection , and availability. RAID 1 Data is mirrored to improve fault tolerance. RAID 1 is used for applications requiring high data availability. RAID 1+0 is also called striped mirror. The basic element of RAID 1+0 is a mirrored pair, which means that data is first mirrored and then both copies of data are striped across multiple HDDs in a RAID set.so that data can be recovered, whereas in RAID 0+1 it is viceversa,a mirrored stripe, If a drive fails , entire stripe is faulted
- 10. RAID 3 RAID 3 stripes data for high performance and uses parity for improved fault tolerance. Parity information is stored on a dedicated drive so that data can be reconstructed if a drive fails. RAID 3 always reads and writes complete stripes of data across all disks, as the drives operate in parallel. It uses byte level striping. RAID 3 is used in large sequential data access , such as video streams. RAID 4 Similar to RAID 3, but uses block level striping. It also has dedicated parity disk, but stripes blocks. RAID 4 provides good read throughput and reasonable write throughput.
- 11. RAID 5 RAID 5 is a very versatile RAID implementation. The main difference bt RAID 4 and 5 is the parity location. In RAID 5, parity is distributed across all disks. It overcomes write bottleneck. RAID 5 is preferred for messaging, data mining, relational database management system (RDBMS) implementations in which (DBAs) optimize data access. RAID 6 RAID 6 implementation requires at least four disks. RAID 6 distributes the parity across all the disks, RAID 5 writes perform better than RAID 6. The rebuild operation in RAID 6 may take longer than that in RAID 5 due to the presence of two parity sets.