Options
Storage question - Can anyone explain RAID 5 parity in human terminology?
ande0255
Banned Posts: 1,178
So I'm running over the storage chapter of Mastering vSphere, and I know it's not a big detail for exam day, but if anyone knows this I would love some clarification for the sake of knowledge (what we at TE live for!!).
It took a bit of time to understand the difference between RAID 1+0 and 0+1, but now I'm onto RAID 5, and after extensive google-fu and reading all sorts of articles including wikipedia on RAID 5 / Parity / XOR calculations I cannot understand what is happening on a RAID 5 array of disks.
Some explanations / diagrams make it seem like a parity bit is written across each disk, some articles made it sounds almost like a Boolean AND'ing only with 1 and 0's representing evens and odds, and in either of those cases I'm not sure what is being written to the parity disk itself that can be deciphered back into usable data.
Is there any simple way of explaining what RAID 5 is? Not sure if I am just tired from reading and my brain is just not accepting any more storage related input for the night, or if these articles I am reading are people with existing knowledge of storage talking on a higher level that I am currently at.
Thanks for whoever reads between refreshing the ESXi 6 thread and drooling over new VMware stuffs
It took a bit of time to understand the difference between RAID 1+0 and 0+1, but now I'm onto RAID 5, and after extensive google-fu and reading all sorts of articles including wikipedia on RAID 5 / Parity / XOR calculations I cannot understand what is happening on a RAID 5 array of disks.
Some explanations / diagrams make it seem like a parity bit is written across each disk, some articles made it sounds almost like a Boolean AND'ing only with 1 and 0's representing evens and odds, and in either of those cases I'm not sure what is being written to the parity disk itself that can be deciphered back into usable data.
Is there any simple way of explaining what RAID 5 is? Not sure if I am just tired from reading and my brain is just not accepting any more storage related input for the night, or if these articles I am reading are people with existing knowledge of storage talking on a higher level that I am currently at.
Thanks for whoever reads between refreshing the ESXi 6 thread and drooling over new VMware stuffs
Comments
-
Options
netsysllc
Member Posts: 479 ■■■■□□□□□□
Raid 5 stripes the data across each of the disks, but uses part of each disk as parity for information for each of the other disks in a reserved area. So lets say you have a 3 disk RAID 5 array. The third disk dies. Your data is (hopefully) still there because disk 1 and 2 both have part of the information for disk 3, when you replace the drive it will rebuild the data from what is on disk 1 and 2. -
Optionsande0255
Banned Posts: 1,178
What confuses me, is the vSphere book makes it sound like there is a dedicated disk in the array called a Parity Disk, that is having this parity information written to it. These are a couple quotes from the book regarding RAID 5:RAID 5 calculates the parity across the drives in the set and writes the parity to another drive.When a drive fails in a RAID 5 set, I/O can be fulfilled using the remaining drives and the parity drive, ...
To further confuse things, the Figure in the book demonstrating a RAID 5 disk array shows the first four disks with bits being written to them, and disk 5 has Parity being written to it. So I'm wondering if you're losing a drive with RAID 5, or if the data is actually striped across all disks and all disks remain usable.
I was jamming through storage until I hit this road block, I really appreciate the input, and big thanks for your response netsys! -
Optionsswefred
Member Posts: 13 ■■■□□□□□□□
This video explains it well:
https://www.youtube.com/watch?v=LTq4pGZtzho -
OptionsLauraMalave
Member Posts: 52 ■■□□□□□□□□
RAID.EDU has nice animations to help visualize the different RAIDs.