7% drive storage penalty for mirroring RAID1? Sound right?

[AMD Die Hard]

I have a K8n Neo2 Platinum with:

2 X 74 GB SATA Western digital raptor drives @ 10,000 rpm running in RAID 1 with the onboard RAID. I only have one partition and windows XP pro reports it as 69.2 GB which is 93.5% of 74 GB.

I am also now running a 4 x ATA133 80 GB Maxtor diamond max 740 in RAID 0,1. For that 320GB of drives, I get 149 GB of storage. Basically a 93.1% of capacity excluding the mirors.

So there is between a 6% and 7% space loss premium for the mirror drives plus the actual miror drives themselves. So for every 100GB worth of drive mirrored, I only get 47 GB. But what the heck at least I will never be subject to the debilitating effects of hard drive failure!

Is this normal? Anyone know?

 

[Bassyhead]

The topic of the differences of between manufacturer's advertised sizes and actual reported size shows up frequently on these forums. When a manufacturer reports their product can store 1 GB, it really means 1,000,000,000 bytes, not one gigabyte. You'll see this in the fine print that they're using metric measurements, not binary. They are not equivalent. A GB is actually 1,073,741,824 bytes. An true gigabyte is about 7% larger than a billion bytes, which is where you're getting your 7%. This discrepency is not limited to RAID setups or any particular filesystems.

 

[AMD Die Hard]

So you think the difference between the 6.5% reduction and the 6.9% reduction is attributable to the manufacturing differences between Maxtor and Western Digital?


The website for the Raptors indicates a formatted capacity of 74,356MB. 7% of that is 69,151 MB, which is what I have BUT isn't formatted capacity listed in MegaBytes just that a formatted capacity in MB?!:| I mean whats the deal on that! Its not like they can say, Oh we meant Gigabytes and you divied by the wrong number of bytes, I mean isnt a MB a MB?

Er, uh apparently not I guess . . . .



WD Website:

Formatted Capacity 74,356 MB
Capacity 74 GB

 

[Bassyhead]

Both the manufacturer and Windows reported values are correct. They are just computed differently. Hard drive manufacturers define a gigabyte as 1000 bytes X 1000 KB X 1000 MB = 1,000,000,000 bytes. Windows, on the other hand, is defining a gigabyte as 1024 bytes X 1024 KB X 1024 MB and you get 1,073,741,824 bytes. Technically, what hard drive manufacturers are using is a GB, and Windows should actually put a "GiB" next to the size, not a "GB". This goes for all hard drives, not any particular brand or filesystem or anything.

You can compute the exact number of bytes your hard drive has yourself. Let's look at the Raptor. On its web page, you'll notice it specifies 74GB, just like on the box. The 74,356 "formatted capacity" was probably rounded to get the 74GB. If you look further down, you'll get the bytes per sector and user sectors per drive. It says "user sectors" because, like all hard drives, some sectors are reserved. Multiply the byte per sector and user sectors for the drive to get the total number of bytes:

512 bytes X 145,226,112 sectors = 74,355,769,344 bytes

What WD is doing is dividing that number by a GB, or 1,000,000,000 bytes (a GB) to get 74.36 GB. Windows, on the other had, divides it by 1,073,741,824 bytes (a GiB) to get 69.25 GB. Both values are correct, just different units. Since a bigger number looks better, hard drive manufacturers use GB.

 

[Howard]

Originally posted by: Bassyhead
The topic of the differences of between manufacturer's advertised sizes and actual reported size shows up frequently on these forums. When a manufacturer reports their product can store 1 GB, it really means 1,000,000,000 bytes, not one gigabyte. You'll see this in the fine print that they're using metric measurements, not binary. They are not equivalent. A GB is actually 1,073,741,824 bytes. An true gigabyte is about 7% larger than a billion bytes, which is where you're getting your 7%. This discrepency is not limited to RAID setups or any particular filesystems.

No, 10^9 bytes is a gigabyte. 2^30 is a gibibyte.

http://physics.nist.gov/cuu/Units/binary.html