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RAID 5 Question

SMURG
By SMURG
in Storage Devices
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Go to solution Solved by wpirobotbuilder,

My understanding is that in RAID 5, for every 2 bits written to the 'useable' space, 1 parity bit gets written to the parity space using an XOR algorithm. This makes perfect sense when you have 3 (say 1TB) drives; you'd have 3TB total with 2TB of useable space and 1TB of parity data.

Thing is, you can have 4 (or more) drives in RAID 5 but you still only need 1 drive's worth of space for parity. Anyone know how this works? Surely if you store 1 parity bit for every 2 bits of data, you need 1.5TB of parity space for 3TB useable space yet somehow you only need 1TB?

The algorithm calculates a single parity block based on block data from all drives, which is stored on the parity drive. So you need one extra drive.

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My understanding is that in RAID 5, for every 2 bits written to the 'useable' space, 1 parity bit gets written to the parity space using an XOR algorithm. This makes perfect sense when you have 3 (say 1TB) drives; you'd have 3TB total with 2TB of useable space and 1TB of parity data.

Thing is, you can have 4 (or more) drives in RAID 5 but you still only need 1 drive's worth of space for parity. Anyone know how this works? Surely if you store 1 parity bit for every 2 bits of data, you need 1.5TB of parity space for 3TB useable space yet somehow you only need 1TB?

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My understanding is that in RAID 5, for every 2 bits written to the 'useable' space, 1 parity bit gets written to the parity space using an XOR algorithm. This makes perfect sense when you have 3 (say 1TB) drives; you'd have 3TB total with 2TB of useable space and 1TB of parity data.

Thing is, you can have 4 (or more) drives in RAID 5 but you still only need 1 drive's worth of space for parity. Anyone know how this works? Surely if you store 1 parity bit for every 2 bits of data, you need 1.5TB of parity space for 3TB useable space yet somehow you only need 1TB?

The algorithm calculates a single parity block based on block data from all drives, which is stored on the parity drive. So you need one extra drive.

I do not feel obliged to believe that the same God who has endowed us with sense, reason and intellect has intended us to forgo their use, and by some other means to give us knowledge which we can attain by them. - Galileo Galilei
Build Logs: Tophat (in progress), DNAF | Useful Links: How To: Choosing Your Storage Devices and Configuration, Case Study: RAID Tolerance to Failure, Reducing Single Points of Failure in Redundant Storage , Why Choose an SSD?, ZFS From A to Z (Eric1024), Advanced RAID: Survival Rates, Flashing LSI RAID Cards (alpenwasser), SAN and Storage Networking

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