Where is the Missing Disk Space on Linux Software Raid

Question

Purchased (4) 2TiB Drives (actual disk space) and created a RAID5 array expecting to have 6TB of useable disk space, however actual useable space is 5.46TiB.

So, the question is where did the disk space go?

First off, I can say for certainty the disks actual useable is verified at 2TB each have mounted and formated on a non-linux system (OSX).

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Disks - 2TB Per disk, Tested HFS, Actual 2TB Useable

root@server:/server# fdisk -l 2>/dev/null | egrep "sd[hijk]" | grep Disk
Disk /dev/sdh: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdj: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdk: 2000.4 GB, 2000398934016 bytes
Disk /dev/sdi: 2000.4 GB, 2000398934016 bytes

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Created RAID5 Array Using (4) Devices Above

/sbin/mdadm --create --verbose /dev/md1 --level=5 --raid-devices=4 /dev/sdh1 /dev/sdi1 /dev/sdj1 /dev/sdk1

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Existing Array

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid5 sdk1[3] sdj1[2] sdi1[1] sdh1[0]
5860535808 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]

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fdisk Info

root@server:/server# fdisk -l /dev/sdh

Device Boot Start End Blocks Id System
/dev/sdh1 1 243201 1953512001 fd Linux raid autodetect

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Block Comparison

Blocks Per Disk * Number of Useable Disks = Total Blocks
1953512001 * 3 = 5860536003

Does Not Match md1 Block Count

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Missing 500G

root@server:/server# pvs | grep md1
/dev/md1 ICYvg lvm2 a- 5.46t 1.96t

Answer 1

Ok, thought I had addressed that above... but your post forced me to go back and do the math:

root@server:/server# fdisk -l 2>/dev/null | egrep "sd[hijk]" | grep Disk 
Disk /dev/sdh: 2000.4 GB, 2000398934016 bytes


2000398934016 bytes = 1.81935224 TiB

1.81935224 TiB *3 = 5.45TiB

So, it is actually the drive size, but the drive is reporting itself at 2000.4GB when it is not and OSX reports it as 2TB when it is not.

Answer 2

2000GB as specified by the manufacturer is only about 1830-ish GB as seen by the computer, because of the difference in the way manufacturers define 1GB vs. the way the computer defines 1GB.

I have a 2TB drive that reads as 1.81TB on the computer.

Computer GB = 1048576000 bytes

Manufacturer GB = 1000000000 bytes