Ext4 partition 8TB

hard drivepartition

Just setup a 8TB disk with gparted as GPT with a single ext4 partition, but now that is mounte it says:
/dev/sdc1 7,3T 38G 6,9T 1% /mnt/BACKUP

Why only 7.3T are available, the ext4 would use the other 700GB?
If I setup multiple partitions I can get more space for data?
i.e. 2 partition of 4 TB would change the situation?

Thanks, BR

Best Answer

Because HDD vendors rarely (if ever) use KiB/MiB/GiB/TiB (x1024) as notation for their storage, but use KB/MB/GB/TB (x1000) instead. Your OS / filesystem uses binary-multiple prefixes, opposed to the industry standard of decimal-multiple prefixes. 

Examples and comparisons with SI prefixes
one mebibyte    1 MiB = 220 Byte = 1,048,576 Byte
one megabyte    1 MB = 106 Byte = 1,000,000 Byte
one gibibyte    1 GiB = 230 Byte = 1,073,741,824 Byte
one gigabyte    1 GB = 109 Byte = 1,000,000,000 Byte
one tebibyte    1 TiB = 240 Byte = 1,099,511,627,776 Byte
one terabyte    1 TB = 1012 Byte = 1,000,000,000,000 Byte


8 TB = 8000000000000 B

Byte based with decimal-multiple prefixes (powers of 10): 
8000000000 KB (kilobyte) 
8000000 MB (megabyte) 
8000 GB (gigabyte) 

8 TB (terabyte) Byte based with binary-multiple prefixes (powers of 2): 
7812500000 KiB (kibibyte) 
7629394.53125 MiB (mebibyte) 
7450.58059692383 GiB (gibibyte) 
7.27595761418343 TiB (tebibyte)

Source: http://wintelguy.com/tb2tib.html

Ext4 adds overhead for sure, but it should be more like ~1,5% of the space.

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