I have 480 GB SSD it currently has the following partitions 256MB EFI partition, 16GB SWAP, and 40GB CentOS 7 see details from lshw below. I want to use the remaining 400GB of unused space on the drive as an iSCSI target. The system only has /dev/sda1, /dev/sda2, /dev/sda3, there is no /dev/sda4 mapped to the 400GB of free disk space on the SSD.

How do I add /dev/sda4 and map it to the unused 400DB on my disk so that it can be used as an iSCSI target? I am on CentOS 7.

          physical id: 1
          logical name: scsi3
          capabilities: emulated
             description: ATA Disk
             product: Crucial_CT480M50
             physical id: 0.0.0
             bus info: scsi@3:0.0.0
             logical name: /dev/sda
             version: MU03
             serial: 13440956E89D
             size: 447GiB (480GB)
             capabilities: gpt-1.00 partitioned partitioned:gpt
             configuration: ansiversion=5 guid=ab9704e2-9162-4c08-a759-956ad6a2f8f1 logicalsectorsize=512 sectorsize=4096
           *-volume:0 UNCLAIMED
                description: Windows FAT volume
                vendor: mkfs.fat
                physical id: 1
                bus info: scsi@3:0.0.0,1
                version: FAT16
                serial: fa26-fbee
                size: 255MiB
                capacity: 255MiB
                capabilities: boot fat initialized
                configuration: FATs=2 filesystem=fat name=EFI System Partition
                description: Linux swap volume
                vendor: Linux
                physical id: 2
                bus info: scsi@3:0.0.0,2
                logical name: /dev/sda2
                version: 1
                serial: c2b0907a-8337-4f32-b1e9-9affe6927264
                size: 15GiB
                capacity: 15GiB
                capabilities: nofs swap initialized
                configuration: filesystem=swap pagesize=4095
                description: data partition
                vendor: Windows
                physical id: 3
                bus info: scsi@3:0.0.0,3
                logical name: /dev/sda3
                logical name: /
                serial: f7efca38-7631-4a20-ae0a-04942971d5ba
                capacity: 39GiB
                configuration: mount.fstype=xfs mount.options=rw,seclabel,relatime,attr2,inode64,noquota state=mounted

fdisk -l output below.

fdisk -l /dev/sda
WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.

Disk /dev/sda: 480.1 GB, 480103981056 bytes, 937703088 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk label type: gpt

#         Start          End    Size  Type            Name
 1         2048       526335    256M  EFI System      EFI System Partition
 2       526336     33294335   15.6G  Linux swap      
 3     33294336    115214335   39.1G  Microsoft basic 
  • Is the disk being listed in fdisk -l ?
    – Stark07
    Aug 11, 2014 at 8:11
  • @AshishKulkarni I have added the output of fdisk -l
    – ams
    Aug 11, 2014 at 12:10

1 Answer 1


The first step is to create a partition. There's no entry in /dev for the free space because it's free space, not a partition.

You can use fdisk to create a partition. Run fdisk /dev/sda, then enter the n command and create a partition covering the free space. Once you're satisfied with the new partition table, enter the command w to write it to disk.

You may need to run partprobe /dev/sda to get the kernel to re-read the partition table.

Now you can add /dev/sda4 to your iSCSI configuration.

  • Better to use gdisk which is like fdisk but for GPT disks. Other than that it works the same as fdisk.
    – MLu
    Aug 12, 2014 at 1:04
  • 1
    @MLu gdisk is also an option, but since the question indicates that fdisk is available and supports GPT partitions, fdisk is fine. Aug 12, 2014 at 1:08

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