ISM V2 Module 3 - Data Protection - Raid

What are commonly used RAID levels?

1. Raid 0 - Striping. 2. Raid 1 - Mirroring. 3. Raid 1+0 - Nested Raid or Striped Mirror. 4. Raid 3 - Parallel Striping with dedicated parity disk. 5. Raid 5 - Striping with distributed parity disk. 6. Raid 6 - Striping with dual-distributed parity disks.

What is RAID and what does it stand for?

It is a technique that combines multiple disk drives into a logical unit (RAID set) and provides protection, performance, or both. Redundant Array of Independent Disks.

What are some common applications that benefit from RAID 1+0?

Performs well for workloads that use small, random, write-intensive I/O's such as: High transaction rate online transaction processing (OLTP). RDBMS temp space.

What are some common applications that benefit from RAID 3?

Provides good performance for applications that involve large sequential data access such as: Data backup. Video streaming.

What is RAID 3? What is the write penalty?

Parallel striped data across a minimum of 3 disks with a dedicated parity disk for fault tolerance. Because the disks write in parallel (all disks write simultaneously), it is slow for random read/writes and is only good for sequential access tasks such as backups or streaming videos. Fault tolerance of 1 disk failure. 4x Write penalty.

RAID - What is parity?

Parity is a method 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. Can be distributed (Raid 5/6) or dedicated (Raid 3).

What are the three types of RAID techniques?

1. Striping. 2. Mirroring. 3. Parity.

What are some common applications that benefit from RAID 5?

Good for random, read intensive I/O applications and preferred for messaging, medium-performance media serving, and RDBMS implementations, in which database administrators (DBAs) optimize data access.

What is Hardware RAID?

Hardware RAID uses a specialized RAID controller that is implemented either on the host or on the array. Disk drives are connected to the RAID controller.

What are the key functions of a RAID Controller?

1. Management and control of disk aggregations. 2. Translation of I/O requests between logical disks and physical disks. 3. Data regeneration in the event of disk failures.

What is a RAID array?

A RAID array is an enclosure that contains a number of disk drives and supporting hardware to implement RAID.

What is a RAID set/group?

A RAID set/group is a subset of disks within a RAID array that can be grouped to form logical associations.

What is a Hot spare?

A hot spare is a spare drive in an array that temporarily replaces a failed disk drive by taking the identity of the failed disk drive.

What is MBTF?

Mean time between failure. Calculated by life expectancy divided by the total number of devices.

What is RAID 1? What is the write penalty?

Mirrored data across two drives. Every write is written to both disks. During disk failure, the mirror drive will be used for access to data and there is no downtime. 2x Write penalty.

RAID - What is mirroring?

Mirroring is a technique whereby the same data is stored on two different disk drives, yielding two copies of the data. If one disk fails, no data is lost.

Total IOPS at peak workload is 1200 Read/Write ratio of 2:1 Calculate the disk load at peak activity for: RAID 1+0 RAID 5 RAID 6

RAID 1+0 - 1600 IOPS RAID 5 - 2400 IOPS RAID 6 - 3200 IOPS

Total IOPS at peak workload is 1600 Read/Write ratio of 3:1 Calculate the disk load at peak activity for: RAID 1+0 RAID 5 RAID 6

RAID 1+0 - 2000 IOPS RAID 5 - 2800 IOPS RAID 6 - 3600 IOPS

Total IOPS at peak workload is 6000 Read/Write ratio of 4:1 Calculate the disk load at peak activity for: RAID 1+0 RAID 5 RAID 6

RAID 1+0 - 7200 IOPS RAID 5 - 9600 IOPS RAID 6 - 12000 IOPS

What is Software RAID?

Software RAID uses host-based software to provide RAID functions and is implemented at the OS level. Benefits include cost and simplicity compared to hardware RAID.

What is Strip size?

Strip size is the number of blocks in a strip, and is the maximum amount of data that can be written to or read from a single disk in the set, assuming that the accessed data starts at the beginning of the strip. Also known as Stripe Depth.

What is Stripe size?

Stripe size = Stripe Depth * Stripe Width

What is RAID 1+0? What is the write penalty?

Striped and Mirrored data across a minimum of 4 disks (2 for striping, and 2 for mirror fault tolerance) and requires an even number of total disks. RAID 1+0 provides improved performance and guarantees a fault tolerance of at least 1 drive, with the possibility for more as long as both the original and mirror disk do not fail. 2x Write penalty.

What is RAID 0? What is the write penalty?

Striped data across a minimum of 2 drives for increased performance with no fault tolerance. No write penalty.

What is RAID 5? What is the write penalty?

Striped data with a distributed parity disk. Provides good performance for random read/writes. Fault tolerance of 1 disk failure. 4x Write penalty.

What is RAID 6? What is the write penalty?

Striped data with dual distributed parity disks. Provides good performance and great fault tolerance with a guaranteed fault tolerance of 2 disk failures. Rebuilds in RAID 6 may take longer due to the presence of a second parity set. 6x Write penalty.

RAID - What is striping?

Striping is a technique of spreading data across multiple drives. Performance benefits.

What is Stripe Width?

The number of disks in a RAID group containing data. Dedicated parity disks are not included in stripe width.