[SLE] How to calculate "lost space" in a RAID5 setup?

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3 total messages Started by JW Wed, 03 Apr 2002 16:17

#155

Author: JW
Date: Wed, 03 Apr 2002 16:17

22 lines
713 bytes

Hey,

We're ordering a large system, and I'm not sure how to calculate how much space is "lost" to redundancy on a RAID 5 system.

Does that make sense?

i.e. if you order five 18GB drives, you don't get 90GB of space, because some of it is used up for redundancy -- you lose x amount of GB.... so how do you figure out "x" ?

        Thanks.

----------------------------------------------------
Jonathan Wilson
System Administrator
Clickpatrol.com
Cedar Creek Software     http://www.cedarcreeksoftware.com


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Re: [SLE] How to calculate "lost space" in a RAID5 setup?

#160

Author: Christopher Mahm
Date: Wed, 03 Apr 2002 14:37

21 lines
705 bytes

* JW (jw@centraltexasit.com) [020403 14:16]:
> i.e.  if you order five 18GB drives, you don't get 90GB of space,
> because some of it is used up for redundancy -- you lose x amount of
> GB....  so how do you figure out "x" ?

(n-1)*p, where n is the number of drives and p is the size of your
smallest disk.  So in your case you'll have roughly 72GB without a
spare and 54GB with.

Keep in mind that while raid 5 is a cost efficient the performance
(at least in my experience) really sucks.

--

-ckm

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Re: [SLE] How to calculate "lost space" in a RAID5 setup?

#157

Author: Stefan Nilsen
Date: Thu, 04 Apr 2002 00:34

15 lines
413 bytes

> i.e. if you order five 18GB drives, you don't get 90GB of space, because
> some of it is used up for redundancy -- you lose x amount of GB.... so how
> do you figure out "x" ?

1 disk is "lost".

/Stefan

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