1.5: Storage Devices: An Overview of RAID

What is the minimum number of drives required to set up RAID 10? What is the number of functional failures? Explain why.

Minimum number of drives: 4 Number of functional failures: 2 (as long as the failures don't happen to the same mirrored pair).

What is the minimum number of drives required to set up RAID 6? What is the number of functional failures? Explain why.

Minimum number of drives: 5 Number of functional failures: 2

What does RAID stand for?

Redundant Array of Independent Disks (Used to be called Redundant Array of Inexpensive Disks)

Name three features of a hardware-based RAID.

1. The RAID is a feature of the hard drive controller (the OS is taken out of the equation). 2. It is either built into the motherboard, or added to the motherboard. 3. Configured outside of the OS. 4. Faster than a software-based RAID.

Name three qualities of a software-based RAID.

1. The RAID is a feature of the operating system. 2. Doesn't require any special hardware. 3. Usually lower-performing than a hardware-based RAID, depending on what other tasks the OS is working on.

Name and describe RAID 1.

Disk Mirroring/Duplexing Disk Mirroring: Two drives are hooked together on one controller. Data is "mirrored"--duplicated on both drives (a primary and backup drive). If primary drive fails, the backup drive kicks in. Disk Duplexing: Same as mirroring, but use one controller per hard drive. It's safer because a controller can fail, and functionality will still be provided. Also faster because each controller only controls one drive.

Name and describe RAID 0. What is the minimum number of drives required to set up RAID 0? What is the number of functional failures? Explain why.

Disk Striping Increases hard drive access speed by saving data to two drives (only has to save half the data to a drive each). It does not provide redundancy, but rather splits data among both drives. If one drive is lost, ALL data is lost. Minimum number of drives: 2 Number of functional failures: 0

Name and describe RAID 5. Name one advantage of this type of RAID.

Disk Striping with Distributed Parity Distributes data and parity information evenly across all drives. This is the fastest way to provide data redundancy.

Name and describe RAID 6. What advantage does this have over RAID 5?

Disk Striping with Extra Parity Same as RAID 5, but with extra parity information. This allows you to lose up to two drives, and still retain information.

What type of RAID does the majority of network servers use?

Either RAID 5 or 6 (Some type of disk striping with parity).

What is one drawback of RAID 5?

If a disk is lost, then extra calculations have to occur to determine which parity information to use, which slows speed.

What is the minimum number of drives required to set up RAID 1? What is the number of functional failures? Explain why.

Minimum number of drives: 2 (can be any number, as long as it's even). Number of functional failures: 1

What is the minimum number of drives required to set up RAID 5? What is the number of functional failures? Explain why.

Minimum number of drives: 3 Number of functional failures: 1

What is the minimum number of drives required to set up RAID 0+1? What is the number of functional failures? Explain why.

Minimum number of drives: 4 Number of functional failures: up to 2 (as long as the failures don't happen to two drives with the same striped data).

Name and describe RAID 0+1.

Nested, Mirrored Stripes RAID 0+1 occurs when you have a pair of two striped drives (four drives total at minimum), and you mirror their data. Has the same functionality/speed as RAID 10.

Name and describe RAID 10.

Nested, Striped Mirrors (Also called RAID 1+0). RAID 10 occurs when you have a pair of two mirrored drives (four drives total at minimum), and you stripe data across them. You get the benefit of speed from striping, and the reliability of mirroring in one.

Are all RAID levels redundant?

No. Not all RAID levels provide redundancy.

How much parity space does a RAID 5 setup use?

One drive's worth of parity space. So, if you have three 2 TB drives, 2 TB will be used for parity (leaving you with 4TB total). If you have four 2 TB drives, 2 TB will still only be used, leaving you with 6 TB total).

When setting up a RAID, what are the two general types that you can choose from?

Software-based RAID, or Hardware-based RAID