Difference between revisions of "Adding a New Disk Drive to an RHEL 6 System"

Revision as of 20:02, 27 October 2016

One of the first problems encountered by users and system administrators these days is that desktop systems and servers tend to run out of disk space to store data. Fortunately disk space is now one of the cheapest IT commodities. In the next two chapters we will look at the steps necessary to configure Red Hat Enterprise Linux 6 to use the space provided via the installation of a new internal disk drive.

Mounted Filesystems or Logical Volumes

There are two ways to configure a new disk drive into a Red Hat Enterprise Linux 6 system. One very simple method is to create one or more Linux partitions on the new drive, create Linux file systems on those partitions and then mount them at specific mount points so that they can be accessed. This approach will be covered in this chapter.

Another approach is to add the new space to an existing volume group or create a new volume group. When RHEL 6 is installed a volume group is created and named vg_hostname, where hostname is the host name of the system. Within this volume group are two logical volumes named lv_root and lv_swap that are used to store the / file system and swap partition respectively. By configuring the new disk as part of a volume group we are able to increase the disk space available to the existing logical volumes. Using this approach we are able, therefore, to increase the size of the / file system by allocating some or all of the space on the new disk to lv_root. This topic will be discussed in detail in Adding a New Disk to an RHEL 6 Volume Group and Logical Volume.

Getting Started

This tutorial assumes that the new physical hard drive has been installed on the system and is visible to the operating system. The best way to do this is to enter the system BIOS during the boot process and ensuring that the BIOS sees the disk drive. Sometimes the BIOS will provide a menu option to scan for new drives. If the BIOS does not see the disk drive double check the connectors and jumper settings (if any) on the drive.

Finding the New Hard Drive in RHEL 6

Assuming the drive is visible to the BIOS it should automatically be detected by the operating system. Typically, the disk drives in a system are assigned device names beginning hd or sd followed by a letter to indicate the device number. For example, the first device might be /dev/sda, the second /dev/sdb and so on.

The following is output from a system with only one physical disk drive:

# ls /dev/sd*
/dev/sda   /dev/sda1  /dev/sda2

This shows that the disk drive represented by /dev/sda is itself divided into 2 partitions, represented by /dev/sda1 and /dev/sda2.

The following output is from the same system after a second hard disk drive has been installed:

# ls /dev/sd*
/dev/sda   /dev/sda1  /dev/sda2 /dev/sdb

As shown above, the new hard drive has been assigned to the device file /dev/sdb. Currently the drive has no partitions shown (because we have yet to create any).

At this point we have a choice of creating partitions and file systems on the new drive and mounting them for access or adding the disk as a physical volume as part of a volume group. To perform the former continue with this chapter, otherwise read Adding a New Disk to an RHEL 6 Volume Group and Logical Volume for details on configuring Logical Volumes.

Creating Linux Partitions

The next step is to create one or more Linux partitions on the new disk drive. This is achieved using the fdisk utility which takes as a command-line argument the device to be partitioned:

# su -
# fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xd1082b01.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help):

As instructed, switch off DOS compatible mode and change the units to sectors by entering the c and u commands:

Command (m for help): c
DOS Compatibility flag is not set
Command (m for help): u
Changing display/entry units to sectors

In order to view the current partitions on the disk enter the p command:

Command (m for help): p

Disk /dev/sdb: 34.4 GB, 34359738368 bytes
255 heads, 63 sectors/track, 4177 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xd1082b01

   Device Boot      Start         End      Blocks   Id  System

As we can see from the above fdisk output the disk currently has no partitions because it is a previously unused disk. The next step is to create a new partition on the disk, a task which is performed by entering n (for new partition) and p (for primary partition):

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 

In this example we only plan to create one partition which will be partition 1. Next we need to specify where the partition will begin and end. Since this is the first partition we need it to start at the first available sector and since we want to use the entire disk we specify the last sector as the end. Note that if you wish to create multiple partitions you can specify the size of each partition by sectors, bytes, kilobytes or megabytes.

Partition number (1-4): 1
First sector (2048-67108863, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-67108863, default 67108863):
Using default value 67108863

Now that we have specified the partition we need to write it to the disk using the w command:

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

If we now look at the devices again we will see that the new partition is visible as /dev/sdb1:

# ls /dev/sd*
/dev/sda  /dev/sda1  /dev/sda2  /dev/sdb  /dev/sdb1

The next step is to create a filesystem on our new partition.

Creating a Filesystem on an RHEL 6 Disk Partition

We now have a new disk installed, it is visible to RHEL 6 and we have configured a Linux partition on the disk. The next step is to create a Linux file system on the partition so that the operating system can use it to store files and data. The easiest way to create a file system on a partition is to use the mkfs.ext4 utility which takes as arguments the label and the partition device:

# /sbin/mkfs.ext4 -L /backup /dev/sdb1
mke2fs 1.41.12 (17-May-2010)
Filesystem label=/backup
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
2097152 inodes, 8388352 blocks
419417 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
256 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000, 7962624

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 36 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Mounting a Filesystem

Now that we have created a new filesystem on the Linux partition of our new disk drive we need to mount it so that it is accessible. In order to do this we need to create a mount point. A mount point is simply a directory or folder into which the filesystem will be mounted. For the purposes of this example we will create a /backup directory to match our filesystem label (although it is not necessary that these values match):

# mkdir /backup

The filesystem may then be manually mounted using the mount command:

# mount /dev/sdb1 /backup

Running the mount command with no arguments shows us all currently mounted filesystems (including our new filesystem):

# mount
/dev/mapper/vg_rhel6-lv_root on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw,rootcontext="system_u:object_r:tmpfs_t:s0")
/dev/sda1 on /boot type ext4 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
/dev/sr0 on /media/RHEL_6.0 x86_64 Disc 1 type iso9660 (ro,nosuid,nodev,uhelper=udisks,uid=500,gid=500,iocharset=utf8,mode=0400,dmode=0500)
/dev/sdb1 on /backup type ext4 (rw)

Configuring RHEL 6 to Automatically Mount a Filesystem

In order to set up the system so that the new filesystem is automatically mounted at boot time an entry needs to be added to the /etc/fstab file.

The following example shows an fstab file configured to automount our /backup partition:

/dev/mapper/vg_rhel6-lv_root /                       ext4    defaults        1 1
UUID=4a9886f5-9545-406a-a694-04a60b24df84 /boot                   ext4    defaults        1 2
/dev/mapper/vg_rhel6-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
LABEL=/backup           /backup                 ext4    defaults        1 2