Hard Drive Format Capacity?

[eRock]

I'm planning on building a new system with a few hard drives I would like to consolidate into 1 Large 2 disk Mirrored RAID Array. I wanted to know if there is a specific formula for calculating the formatted capacity for a drive. I want to format in NTFS and need to know how large of a drive I will need!

[ImaNihilist]

Formatting really doesn't take up any space. The "perceived" space loss is a result of the conversion from base-10 (how HDD manufactures list space) to base-2 (how the computer writes/reads data).

If you want to know how much space you'll be able to use, just multiply the HDD specified space by a value of 0.93 (or to be entirely accurate, 0.93132257462). The formatting method (FAT/FAT32/NTFS/HFS etc.) doesn't really matter. Just multiply by 0.93.

Technically, GB (gigabyte) stands for base-10 and GiB (gigibyte) stands for the base-2. When you click on My Computer and view your space, while it says GB, it's actually GiB. No one really uses GiB though, and so GB ends up standing for both, and that's where the confusion is.

1GB = 1,000,000,000 bytes (how HDDs are manufactured)
1GiB = 1,073,741,824 bytes (how software actually sees and uses HDD space)

40GB = 37GiB
80GB = 74GiB
100GB = 93GiB
120GB = 111GiB
160GB = 148GiB
200GB = 186GiB
250GB = 232GiB
300GB = 279GiB
320GB = 297GiB
400GB = 372GiB
500GB = 465GiB
750GB = 697GiB
1000GB = 930GiB

[Steve R Jones]

Or simply put, using round numbers, if you use two 100 gig drives in a RAID 0 you'll have 200 gig of drive space.

If you were to do the NOT recommended method of using a 60 gig and a 100 gig drive, you'll end up with 120gigs thus loosing 40 gigs.

Course you know the part about if one drive dies you loose ALL data don't you?

[kent1146]

Or simply put, using round numbers, if you use two 100 gig drives in a RAID 0 you'll have 200 gig of drive space.

If you were to do the NOT recommended method of using a 60 gig and a 100 gig drive, you'll end up with 120gigs thus loosing 40 gigs.

Course you know the part about if one drive dies you loose ALL data don't you?

"2 disk Mirrored Raid Array" != RAID-0


And to eRock:
If you build a "mirrored" RAID array, you are using RAID-1. That means that 2x 500GB hard drives in a "mirrored" array will equal 500GB of useable space.

[ua549]

I read "1 Large 2 disk Mirrored RAID Array" as 4 drives. IOW RAID 0+1.

[Dorbel Tweeter]

I read "1 Large 2 disk Mirrored RAID Array" as 4 drives. IOW RAID 0+1.

Why on Earth would you read "1 Large 2 disk Mirrored RAID Array" as meaning 4 drives in a RAID 0+1 configuration????

The word "Large" is irrelevant. The word "1" means there is going to be 1 RAID array.
"2 disk Mirrored RAID Array" means "2 disk Mirrored RAID Array". Duh.

A "2 disk Mirrored RAID Array" is a RAID level 1 array. Period.

The OP was asking about a formula for determining formatted capacity. Why introduce this confusion??

[Dorbel Tweeter]

"2 disk Mirrored Raid Array" != RAID-0

Correct.

And to eRock:
If you build a "mirrored" RAID array, you are using RAID-1. That means that 2x 500GB hard drives in a "mirrored" array will equal 500GB of useable space.

Not correct. ImaNihilist answered the OP's question, which was about formatted capacity, quite well. If he puts 2 500GB hard drives in a mirrored RAID 1 array, he's going to get 465GB usable formatted capacity, not 500GB.

[iamsostupid]

holy cow WWYBYWB