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In short it combines striping with parity check bits that are spread out over the disks, a minimum of 3 drives is needed. The advantage over RAID 0 is that 1 drive can fail and the array will still function (more slowly).

The main disadvantage is that the check bits require quite a bit of processing which on motherboard based RAID controllers and cheaper RAID cards is carried out by the host computers CPU, this makes it a poor choice unless you invest in a decent RAID controller.

RAID 5
 

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Discussion Starter · #4 ·
So if I have 3 1tb drives, how much storage will show in my OS?
I'm about to make a little server box
so thts why I'm asking
 

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you will get slow writes if you use onboard controllers as the CPU has to calculate the parity bits, if you are going to do RAID-5 then get a dedicated controller like the dell PERCi5
My RAID-5 arrray 4x1TB WD green drives
 

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Quote:

Originally Posted by moward View Post
you will get 2TB with 3 x 1TB drives

space efficiency for RAID 5 is calculated using 1-1/n
where n is the no. of drives.
Isn't it just N-1?

RAID5 read performance is near n-1.
RAID5 write performance is bad... something like 20-80MB/s with host-based RAID controller.

RAID5 is good for media storage since its usage would be write once, read many.
 

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Quote:

Originally Posted by moward View Post
space efficiency for RAID 5 is calculated using 1-1/n
where n is the no. of drives.

Quote:

Originally Posted by DuckieHo View Post
Isn't it just N-1?
moward is talking efficiency, not capacity.

The capacity of an n-drive RAID5 array is:
(no of drives - 1) x capacity of smallest drive
= n-1 (assuming all drives equal size)

The storage efficiency of an n-drive array the array is:
number of drives containing data (n-1) / total number of drives (n)
= (n-1)/n (assuming all drives equal size)

The efficiency is an indicator of how much space you have to pay for in order to store a certain amount of data.
= 1 - 1/n
 
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