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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).


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


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


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]


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


Block Comparison

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

Does Not Match md1 Block Count


Missing 500G

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

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2 Answers 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

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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.

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