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I have a server with these characteristics:

CPU: Intel Core i7-2600
PLUSRAID Controller 4-Port SATA PCI-E - Adaptec 5405

One each, SATA SSD, 240 GB

Two each, SATA HDDs, 3.0 TB Enterprise

Two each, 8 GB DDR3 RAM

I installed Ubuntu on it, but it shows the space such as this, far less than the true capacity:

root@ns1 /boot # lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:16 1 238.4G 0 disk
├─sdb2 8:18 1 512M 0 part
│ └─md1 9:1 0 511.4M 0 raid1 /boot
├─sdb3 8:19 1 229.9G 0 part
│ └─md2 9:2 0 229.8G 0 raid1 /
└─sdb1 8:17 1 8G 0 part
 └─md0 9:0 0 8G 0 raid1 [SWAP]
sda 8:0 1 2.7T 0 disk
├─sda2 8:2 1 512M 0 part
│ └─md1 9:1 0 511.4M 0 raid1 /boot
├─sda3 8:3 1 229.9G 0 part
│ └─md2 9:2 0 229.8G 0 raid1 /
└─sda1 8:1 1 8G 0 part
 └─md0 9:0 0 8G 0 raid1 [SWAP]

and

root@ns1 /boot # df -lh
Filesystem Size Used Avail Use% Mounted on
udev 7.8G 0 7.8G 0% /dev
tmpfs 1.6G 5.3M 1.6G 1% /run
/dev/md2 226G 17G 198G 8% /
tmpfs 7.8G 0 7.8G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 7.8G 0 7.8G 0% /sys/fs/cgroup
/dev/md1 488M 176M 287M 38% /boot
tmpfs 1.6G 0 1.6G 0% /run/user/0

I don't seem to be using all the space available on the sda disk at all, the two 3 terabytes disks.

What am I doing wrong?

Thanks!

It looks like that you have made raid1 (mirror) between partitions on your SSD and HDD. This is not best practice, since it more or less restricts performance to that of the slowest disk.

You can see that /boot, / and [ SWAP ] is defined on partitions on both /dev/sda and /dev/sdb.

sdb 8:16 1 238.4G 0 disk
├─sdb2 8:18 1 512M 0 part
│ └─md1 9:1 0 511.4M 0 raid1 /boot
├─sdb3 8:19 1 229.9G 0 part
│ └─md2 9:2 0 229.8G 0 raid1 /
└─sdb1 8:17 1 8G 0 part
 └─md0 9:0 0 8G 0 raid1 [SWAP]
sda 8:0 1 2.7T 0 disk
├─sda2 8:2 1 512M 0 part
│ └─md1 9:1 0 511.4M 0 raid1 /boot
├─sda3 8:3 1 229.9G 0 part
│ └─md2 9:2 0 229.8G 0 raid1 /
└─sda1 8:1 1 8G 0 part
 └─md0 9:0 0 8G 0 raid1 [SWAP]

I would recommend that you reinstall Ubuntu using only SSD for /boot, / and SWAP. If yopu really want a raid1/mirror setup, you should buy one more 240 GB SSD, so you mirror between similar type and size disks.

Anyway .. if you take a look at your disks with gparted (or fdisk -l) you should see a huge unallocated amount of data on /dev/sda.

The reason why your "3,0 TB" drive (sda) shows up as 2.7T is most likely due to different units being used.

The size is probably about 2.7 Tebibyte, which is approximately the same as 3.0 TB.

You can read about it here: https://en.wikipedia.org/wiki/Tebibyte

lsblk shows all disk partitions, while df -lh only shows your mounted partitions.