ISMv3 4.3
What is the minimum number of disks required for a RAID 1 + 0?
4
If RAID 3 has the same minimum number of disks, available storage capacity %, write penalty, and protection type as RAID 5, what makes it inferior?
It always reads and writes complete stripes of data across all disks because the drives operate in parallel. This creates a bottleneck in performance, because it cannot service multiple requests simultaneously.
What are the commonly used RAID levels?
- RAID 0 - RAID 1 - RAID 1 + 0 - RAID 3 - RAID 5 - RAID 6
What are the two implementation methods of RAID?
- Software RAID - Hardware RAID
What are the three different RAID techniques that form the basis of defining various RAID levels?
- Striping - Mirroring - Parity
How does a RAID improve storage system performance?
By serving I/Os from multiple drives simultaneously.
What is hot sparing?
A process that temporarily replaces a failed disk within a disk drive with a spare drive in a RAID array by taking the identity of the failed disk drive.
That is striping?
A technique of spreading data across multiple drives in order to use the drives in parallel.
What is the purpose of mirroring?
It provides data protection.
Does striping offer data protection?
No, unless parity or mirroring is used.
How does strip size affect data?
The smaller the strip size, the smaller the pieces of data spread across the disks in the RAID set.
What are the key functions of RIAD controllers?
- 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
What are the limitations of software RAID?
- Performance - Supported features (types of RAID levels) - Operating system compatibility
What is a software RAID?
A RAID system that uses compute system-based software to provide RAID functions and is implemented at the operating-system level.
What is hardware RAID?
A RAID system that uses specialized hardware controllers that are either implemented on the compute system or on the storage system.
What is RAID 6?
A RAID technique that stripes data across all disks, distributes parity across all disks, but also includes a second parity element. This allows two disks to fail and still offer data protection.
What is RAID 3?
A RAID technique that stripes data across disks, and has a dedicated parity disk.
What is RAID 5?
A RAID technique that stripes data across disks, but does not have a dedicated parity disk. Instead, parity is distributed across all disks.
What is a Redundant Array of Independent Disks?
A technique that combines multiple disk drives into a logical unit (RAID set) and provides protection, performance, or both.
What is parity?
A technique to protect striped data from disk drive failure without the cost of mirroring. An additional disk drive is added to hold parity, a mathematical construct that allows re-creation of the missing data.
What is mirroring?
A technique whereby the same data is stored on two different disk drives, yielding two copies of the data.
What is a RAID array?
An enclosure that contains a number of disk drives and supporting hardware to implement RAID.
What happens in a RAID array that uses hot sparing, when the failed disk is replaced.
Data from the hot spare is copied to it, and the hot spare returns to its idle state, ready to replace the next failed drive. (Alternatively, the hot spare becomes the permanent drive and the replacement drive becomes teh hot spare.)
What is the minimum number of disks, available storage capacity %, write penalty, and protection type of RAID 1?
Min. Disks: 2 Available Storage Capacity: 50% Write penalty: 2 Protection: Mirror
What is the minimum number of disks, available storage capacity %, write penalty, and protection type of RAID 3?
Min. Disks: 3 Available Storage Capacity: [(n-1)/n]*100 Write penalty: 4 Protection: Parity (supports single disk failure)
What is the minimum number of disks, available storage capacity %, write penalty, and protection type of RAID 5?
Min. Disks: 3 Available Storage Capacity: [(n-1)/n]*100 Write penalty: 4 Protection: Parity (supports single disk failure)
What is the minimum number of disks, available storage capacity %, write penalty, and protection type of RAID 1+0?
Min. Disks: 4 Available Storage Capacity: 50% Write penalty: 2 Protection: Mirror
What is the minimum number of disks, available storage capacity %, write penalty, and protection type of RAID 6?
Min. Disks: 4 Available Storage Capacity: [(n-2)/n]*100 Write penalty: 4 Protection: Parity (supports two disk failures)
What technique does RAID 1 use?
Mirroring
How does data protection differ from data backup?
Mirroring provides captures changes in data, whereas a backup captures point-in=time images of the data.
What are other names for RAID 1 + 0?
RAID 10 (Ten) RAID 1/0 Striped Mirror
What technique does RAID 0 use?
Striping
What is RAID 1 + 0?
Striping and Mirroring
What is strip size (AKA stripe depth)?
The number of blocks in a strip (the portion of a stripe that is written to a single disk in the set).
What is stripe width?
The number of data strips in a stripe.
How is stripe size calculated in a parity strip?
The strip size is multiplied by all disks EXCEPT for the parity strip.
How does a RAID provide data protection?
Through the use of redundant drives and parity.
What is the affect on read and write speeds in mirroring?
Write speed is slightly lowered, read speed is increased.