Raid 5 Capacity

Spire · Posted: Wed, 10 Mar 2004 01:50:04 Post Subject: Raid 5 Capacity

If I use 3 80 gig drives in Raid 5 array, what will my total capacity be??? (Disregard formatting losses)

80 gig???
160 gig???
240 gig???

I understand the fact that parity is stored on a different drive, but what will the total be??

I sent the 2 80 deathstars back, and am looking at getting 3 different SATA drives.

80's or 120's????

T-shirt · Posted: Wed, 10 Mar 2004 05:36:11 Post Subject:

you'd end up with 160Gb's of usable space.
RAID distributes the parity on all the drives in the array.
data is totally recoverable, even after the loss of one drive but uses one drive worth of space
As far as size, shop by price, I'm sure you'll be able to fill the space.
you might actually want to by 4, with one as a spare

BeerCheeze · Posted: Wed, 10 Mar 2004 19:25:44 Post Subject:

Like T said...

One thing to note... Raid 5 is pretty slow. Because of the overhead of calculating the parity.

knight0334 · Posted: Wed, 10 Mar 2004 19:51:17 Post Subject:

Dud3! · Posted: Wed, 10 Mar 2004 20:28:09 Post Subject:

Why 5 Spire?

Spire · Posted: Wed, 10 Mar 2004 21:02:21 Post Subject:

Faster than 1 and safer than 0, I guess.

I was not aware of the speed hit for level 5. I realize it would be slower than 0 but should still be faster than 1 right???

BeerCheeze · Posted: Wed, 10 Mar 2004 23:10:54 Post Subject:

No, 5 is never faster than 1 or 0. Doesn't matter the controller or the drives. If you compare apples to apples, you will always lose speed with RAID 5. RAID 5 is used to allow large storage with no down time. It is not designed for speed.

Think about it...

RAID 0 - The controller simply splits the data into multiple drives. Little to no intelligence involved.

RAID 1 - The controller simply writes the same data twice. Again, little to no intelligence involved.

RAID 5 - The controller has to write the data across multiple drives, keeping track of what it has written Do the math on it and the write another bit on the other drive to make the parity either even or odd, depending on the setup.

Here is how RAID 5 works. Let's say you have 5 drives, and one is the parity drive, so you are writing across 4 drives. Let's say it's using even parity. So when you do a write on the drive let's just say it write:

Drive 1: 0
Drive 2: 0
Drive 3: 1
Drive 4: 1

It now has to do the math, 0+0+1+1 = 2 or EVEN so on drive 5 it would write a 0.

Now reading from RAID 5 isn't too bad, but again lot's of overhead having to reassemble all that. However when you lose a drive... it is a LOT slower. Because it has to read everything into it's buffer, do the math and add the missing bit. But... you're still up and operational even after a HDD failure.

Dud3! · Posted: Thu, 11 Mar 2004 00:28:07 Post Subject:

That's why I asked why he wanted 5, it's not something you use for a home computer. Is this for you server Spire? In that case....

Spire · Posted: Thu, 11 Mar 2004 01:09:56 Post Subject:

Yea this would be for SPIRESERVER that doesn't exist yet.

The Raptors in RAID 0 are working JUUUUST fine in SPIREMACHINE!!!!

Thanks for the info EC!!!

In raid 1, 2x80's =80
In RAID 5, 3x80's =160

Having 80 gig of backed up data isn't enough. So I guess I have to figure out if I get 2x160's or 3x80's then.

T-shirt · Posted: Thu, 11 Mar 2004 13:27:57 Post Subject: