i have just purchased 3x250 WD hardisks
In order to configure RAID5 on my Debian machine with mdadm util.



I dont know why but at the begining i had 2 disks with ATA and the third disk with SATA allwayse at the same point the PC were stucked when i had created the RAID therefore i have replace the SATA disk and get 3rd ATA inplace.


my question is the following:
i have notice that fdisk identify the HDs as 250GB
now i have removed the RAID and make xfs Filesysten and
and when i makefs.xfs /dev/hdc1 (the 250GB) i recieve 234GB partition rather than 250Gb
so actualy i dont know why but i losing 16 gb ?? :-(



maybe it depends on CHS/LBA/Auto/Large 16Heads 15 Heads and so on ??
I really dont know what to do ??

Any idea. ??

Best regards

Nothing's wrong with your setup or the numbers you are seeing.

Manufactures use “decimal capacity” to describe drive capacities, whereas almost all linux/windows utilities report “binary capacity”. Systems almost always report a smaller drive size than the manufacturers report.

Decimal Capacity: 1GB = 1,000,000,000 bytes

Binary Capacity: 1GB = 1,073,741,824 bytes

The decimal logic is fairly obvious, but it doesn't match physical reality. You can't have exactly 1000 bytes on a disk when the minimal disk subdivision is 512 bytes. but you can have 1024 bytes (2 x 512).

This is the binary logic:

1KB = 1024 bytes
1MB = 1024 KB
1GB = 1024 MB
1GB = 1024 MB/GB * 1024 KB/MB * 1024 bytes/KB = 1,073,741,824 bytes

So:

1 binary GB = 1.073741824 decimal GB