RAID6 Volume size

[nry]

I have 8x Hitachi 5K3000 3TB disks in RAID6 on my Areca controller.

On the controller these show as 18000.0GB
In Ubuntu it shows as 18000.0GB in fdisk

Disk /dev/sdb: 18000.0 GB, 17999997173760 bytes
255 heads, 63 sectors/track, 273546 cylinders, total 4394530560 sectors
Units = sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00000000

But when formatted this is showing as 16.76 TB
I work this out as 17162GB (16.76 x 1024), assuming that's correct?

So providing I am not missing something obvious here, I should have my full 18000GB available resulting in 17.57 TB

Where has my 0.81TB gone?

Sorry if I have completely miscalculated this! Running on under 5 hours sleep today haha

 

[drescherjm]

The difference is probably caused by the difference between TB and TiB.

http://www.unitjuggler.com/convert-memory-from-TB-to-TiB.html

 

[nry]

Hate these conversions! So really it should say Tb and not TB (TiB)

 

[DieTa]

Wouldn't Tb be Terabits?

 

[houkouonchi]

dmesg/syslog shows you both clear as day:

Jan 15 01:11:52 dekabutsu sd 0:0:0:0: [sda] 251947008 512-byte logical blocks: (128 GB/120 GiB)
Jan 15 01:11:52 dekabutsu sd 0:0:0:1: [sdb] 58586112 512-byte logical blocks: (29.9 GB/27.9 GiB)
Jan 15 01:11:52 dekabutsu sd 0:0:0:1: [sdb] Write Protect is off
Jan 15 01:11:52 dekabutsu sd 0:0:0:1: [sdb] Mode Sense: cb 00 00 08
Jan 15 01:11:52 dekabutsu sd 0:0:0:2: [sdc] 251947008 512-byte logical blocks: (128 GB/120 GiB)
Jan 15 01:11:52 dekabutsu sd 0:0:0:1: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 15 01:11:52 dekabutsu sd 0:0:0:2: [sdc] Write Protect is off
Jan 15 01:11:52 dekabutsu sd 0:0:0:2: [sdc] Mode Sense: cb 00 00 08
Jan 15 01:11:52 dekabutsu sd 0:0:0:2: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 15 01:11:52 dekabutsu sd 0:0:0:3: [sdd] 85374958592 512-byte logical blocks: (43.7 TB/39.7 TiB)
Jan 15 01:11:52 dekabutsu sd 0:0:0:3: [sdd] Write Protect is off
Jan 15 01:11:52 dekabutsu sd 0:0:0:3: [sdd] Mode Sense: cb 00 00 08
Jan 15 01:11:52 dekabutsu sd 0:0:0:3: [sdd] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 15 01:11:52 dekabutsu sd 1:0:1:0: [sde] 164062474240 512-byte logical blocks: (83.9 TB/76.3 TiB)
Jan 15 01:11:52 dekabutsu sd 1:0:1:0: [sde] Write Protect is off
Jan 15 01:11:52 dekabutsu sd 1:0:1:0: [sde] Mode Sense: cb 00 00 08
Jan 15 01:11:52 dekabutsu sd 1:0:1:0: [sde] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA