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-   -   How does raid5 work? (http://www.hardwarecanucks.com/forum/storage/39601-how-does-raid5-work.html)

Blu January 5, 2011 10:26 AM

How does raid5 work?
I've heard from people that raid 5 will protect all your data on both drives but how exactly? What if I got 3 2TB Drives in there will I only get to use 3TB of space? Still doesn't make alot of sense to me, cause if the one 2TB drive fails then I only have 1TB left on another drive to save me...How does this work I'm stumped...Is raid 10 the best way to go for the fastest and surfire way of always having a backup?

Squeetard January 5, 2011 10:55 AM

Raid 10 needs 4 drives. 2 striped for speed that are also mirrored to the other 2. Raid 5 is a stripe that uses parity to check and correct errors, the same way you use parity files to fix incomplete downloads (cough cough). So the raid controller reserves space on each drive for the parity data.

bojangles January 5, 2011 11:11 AM

I think all it took was an easy google search, but here you go...

RAID - Wikipedia, the free encyclopedia

YouTube - RAID 5 & RAID 10 Tutorial & Explanation (NCIX Tech Tips #79)

Empty_Quarter January 5, 2011 11:20 AM

RAID-5 and higher (except 10) are excellent solutions for both speed and protection, however I would only suggest you do it if you have a dedicated hardware RAID card.

I'd do RAID-6 if you are willing to go the hardware RAID route, it is fairly new but is a standard on all new cards.

Unfortunately, for RAID-6 to be efficient, you need 5+ drives. If you have 3 drives, RAID-5 suffices, and if you have 4, RAID-5 and 10 works.

Linus explains all else well.

Blu January 5, 2011 11:35 AM

Still have a few questions about it...so it's sort of like how you can repair files on usenet without them being that exact size...Still confused as I'm loosing say 2tb, whats to say the drive has that exact 2TB that I lost and not 1TB of drive 1 and 1TB of drive 2?...I dunno man this is like magical and stuff, hard to understand :(. I mean I get what happens, if I loose a drive in raid 5 I can swap out the dead disk and rebuild the array (also how would I tell what drive died?...would I just keep removing them till I found out what drive was dead or...?)

Let me copy my post from ncix,

So let me get this straight, if I have 3 2TB Drives running in raid 5, and one fails, anyone of them fail. I just need to swap in another 2TB and I'm fine? I really don't get how this works, what if the information I got on the "backup" drive isn't what was on the drive that died? I'm still sort of new to this as I just learned how to use usenet and figured the repair was magical since I never figured it out, raid 1 makes sense to me since there is constantly a full back up of the data you have, raid 5 to me makes it like I only have 50% of a backup?...or does it compress the data somehow?

Also lets do this for example, I have the following set up,

8 2TB Drives in raid5 - how much storage do I have?

bojangles January 5, 2011 11:45 AM

You'll have 7x2TB of storage to use. The parity bits are a check that makes sure that the data for that stripe on the drives is correct. If a hard drive fails, that data can be recovered because the parity bit will allow reconstruction of the corrupted data. Instead of having all the backup on one drive, it's spread across all of them.

LarkStarr January 5, 2011 11:52 AM

Parity bit - Wikipedia, the free encyclopedia

gingerbee January 5, 2011 12:10 PM

RAID - Wikipedia, the free encyclopedia

bojangles January 5, 2011 12:10 PM


Originally Posted by LarkStarr (Post 470837)

That explains everything. Nice tip for Blu!

Empty_Quarter January 5, 2011 12:17 PM


Originally Posted by Blu (Post 470828)
I mean I get what happens, if I loose a drive in raid 5 I can swap out the dead disk and rebuild the array (also how would I tell what drive died?...would I just keep removing them till I found out what drive was dead or...?)

The RAID controller (onboard software or hardware) will tell upon boot which drive is dead, usually by the drive's ID (that the manufacturer gave it, not what you put in windows).

If a HDD does die, you replace it, and the raid controller will use parity data on the remaining drives to build the new drive. The quality and speed of the rebuilding process is Dependant on your controller.

In raid 5, whatever number of drives you have, you lose 1 drive, so n-1. In raid-6, you lose 2 drives.

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