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Old 10-15-2005, 09:50 PM   #1
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WD250 Gb Problem with Disk Size

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
Old 10-16-2005, 02:10 AM   #2
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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


1 binary GB = 1.073741824 decimal GB

Last edited by WhatsHisName; 10-16-2005 at 02:15 AM.


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