bjrod20
Posts: 2
Joined: Sat Apr 18, 2015 4:33 am

2TB HD ext4 showing only 1.8TB available

Sat Apr 18, 2015 5:00 am

Hi. First post and a noob question - sorry if this is posted to the wrong section.

I'm trying to set up a RPi2 as a backup server. I had a 2TB HD formatted as Mac OS Extended (Journaled) that I reformatted in the Mac to MS DOS. I attached it to the RPi2, and using the instructions at http://blog.amitparekh.com/?p=31, I formatted the drive as ext4, however, the drive is now showing only a 1.8TB partition.

How do I make the partition use the whole 2TB?

If it helps, the following is shown in the various disk utilities:

Code: Select all

sudo blkid
/dev/sda1: LABEL="disk1" UUID="[edit]" TYPE="ext4"


sudo fdisk -l
Disk /dev/sda: 2000.4 GB, 2000398934016 bytes
81 heads, 63 sectors/track, 765633 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048  3907029167  1953513560   83  Linux


sudo parted -l
Model: WDC WD20 EARX-00PASB0 (scsi)
Disk /dev/sda: 2000GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  2000GB  2000GB  primary  ext4


sudo sfdisk -l -uM
Disk /dev/sda: 243201 cylinders, 255 heads, 63 sectors/track
Units = mebibytes of 1048576 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start   End    MiB    #blocks   Id  System
/dev/sda1         1  1907729- 1907729- 1953513560   83  Linux
/dev/sda2         0      -      0          0    0  Empty
/dev/sda3         0      -      0          0    0  Empty
/dev/sda4         0      -      0          0    0  Empty


sudo cfdisk
Partition Table for /dev/sda

         ---Starting----      ----Ending-----    Start     Number of
 # Flags Head Sect  Cyl   ID  Head Sect  Cyl     Sector    Sectors
-- ----- ---- ---- ----- ---- ---- ---- ----- ----------- -----------
 1  0x00   32   33     0 0x83   62   63 765633        2048  3907027120
 2  0x00    0    0     0 0x00    0    0     0           0           0
 3  0x00    0    0     0 0x00    0    0     0           0           0
 4  0x00    0    0     0 0x00    0    0     0           0           0


lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda           8:0    0   1.8T  0 disk
└─sda1        8:1    0   1.8T  0 part /media/disk1


df -h
Filesystem                 Size  Used Avail Use% Mounted on
rootfs                     7.2G  496M  6.4G   8% /
/dev/root                  7.2G  496M  6.4G   8% /
devtmpfs                   484M     0  484M   0% /dev
tmpfs                       98M  228K   98M   1% /run
tmpfs                      5.0M     0  5.0M   0% /run/lock
tmpfs                      195M     0  195M   0% /run/shm
/dev/mmcblk0p1              48M   15M   34M  30% /boot
/dev/sda1                  1.8T  1.7T   99M 100% /media/disk1
tmpfs                      195M     0  195M   0% /tmp

User avatar
xoopha
Posts: 106
Joined: Mon Feb 09, 2015 9:52 pm

Re: 2TB HD ext4 showing only 1.8TB available

Sat Apr 18, 2015 1:59 pm

2 terabytes = 2000 gigabytes = 1.81 binary terabytes, which is what the computer reports.
Last edited by xoopha on Sat Apr 18, 2015 11:21 pm, edited 1 time in total.

User avatar
DougieLawson
Posts: 36578
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website Twitter

Re: 2TB HD ext4 showing only 1.8TB available

Sat Apr 18, 2015 3:19 pm

Look at the difference between KB and KiB, MB and MiB and TB & TiB.

One set of measures use multiples of base 2. 1Ki = 1024, 1Mi = 1024*1024, 1Ti = 1024*1024*1024
The other set of measures use multiples of base 10. 1K = 1000, 1M = 1000*1000, 1T = 1000*1000*1000

It's done to confuse, it's done so that the marketing dept. for the disk makers can sell a drive as 2TB when it only holds 1.8TiB.

It works much the same way that items get priced at £19.99 rather than £20 (or £19 19s 6d in old money before Feb 1971). The confusion plays against the punter who's buying the short measure for a penny lower price.
Note: Having anything humorous in your signature is completely banned on this forum. Wear a tin-foil hat and you'll get a ban.

Any DMs sent on Twitter will be answered next month.

This is a doctor free zone.

User avatar
mikronauts
Posts: 2732
Joined: Sat Jan 05, 2013 7:28 pm
Contact: Website

Re: 2TB HD ext4 showing only 1.8TB available

Sat Apr 18, 2015 10:26 pm

The posts are correct, disk capacity is reported in interesting ways. You may still be able to recover some reserved space.

Normally, mkfs reserves 5% of the drive for root, which makes sense when the drive is the root partition (so log files can still be written when a user fills the disk)

sudo tune2fs -m 0 /dev/sdaXXXXXX

recovers the reserved space.

For more on tune2fs see http://www.unixtutorial.org/commands/tune2fs/
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

bjrod20
Posts: 2
Joined: Sat Apr 18, 2015 4:33 am

Re: 2TB HD ext4 showing only 1.8TB available

Sun Apr 19, 2015 3:12 am

Many thanks for your responses. It seems obvious now in hindsight. From you pointing me in the right direction I've also learnt that if I'd used df --si or df -H it would have given me the figures in powers of 1000 not 1024.
mikronauts wrote:You may still be able to recover some reserved space.
sudo tune2fs -m 0 /dev/sdaXXXXXX
This is interesting to know. Thanks.

Return to “Beginners”