AWS : Attaching Amazon EBS volume to an instance

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Amazon EBS volume

Each Amazon EC2 instance that we launch has an associated root device volume, either an Amazon Elastic Block Store (Amazon EBS) volume or an instance store volume. We can use block device mapping to specify additional Amazon EBS volumes or instance store volumes to attach to an instance when it's launched.

We can also attach additional Amazon EBS volumes to a running instance.

We can attach our Amazon EBS volume to one of our instances in the same Availability Zone.

To attach an Amazon EBS volume to an instance (we're using CentOS 7) using the console:

Open the Amazon EC2 console.
Click Volumes in the navigation pane.
Select a volume and then click Attach Volume.

In the Attach Volume dialog box, start typing the name or ID of the instance to attach the volume to in the Instance box, and select it from the list of suggestion options (only instances in the same Availability Zone as the volume are displayed). Encrypted volumes can only be attached to instances that support Amazon EBS encryption.
Verify that the suggested device name is suitable, or enter a device name in the Device box.

Click Attach to attach the volume to the instance. The volume and instance must be in the same Availability Zone. We should see the following in the "Description" tab of the instance:

Making an Amazon EBS Volume Available for Use

After we attach an Amazon EBS volume to our instance, it is exposed as a block device. We can format the volume with any file system (mkfs) and then mount it (mount). After we make the EBS volume available for use, we can access it in the same ways that we access any other volume.

Making the Volume Available on Linux

Use the following procedure to make an Amazon EBS volume available for use on Linux:

Connect to our instance using SSH.

$ ssh -i my_aws_pem.pem centos@54.210.155.188
[centos@ip-172-31-61-253 ~]$

Depending on the block device driver of the kernel, the device might be attached with a different name than what we specify. For example, if we specify a device name of /dev/sdh, our device might be renamed /dev/xvdh or /dev/hdh by the kernel; in most cases, the trailing letter remains the same. In some versions of Red Hat Enterprise Linux (and its variants, such as CentOS), even the trailing letter might also change (where /dev/sda could become /dev/xvde). In these cases, each device name trailing letter is incremented the same number of times. For example, /dev/sdb would become /dev/xvdf and /dev/sdc would become /dev/xvdg. Amazon Linux AMIs create a symbolic link from the renamed device path to the name we specify, but other AMIs might behave differently.
Use the lsblk command to view our available disk devices and their mount points (if applicable) to help us determine the correct device name to use.
```
$ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   8G  0 disk 
└─xvda1 202:1    0   8G  0 part /
xvdf    202:80   0   1G  0 disk 
```
The output of lsblk removes the /dev/ prefix from full device paths. In this example, /dev/xvda1 is mounted as the root device (note the MOUNTPOINT is listed as /, the root of the Linux file system hierarchy), and /dev/xvdf is attached, but it has not been mounted yet.

We can get more detailed info from fdisk command:
```
$ sudo fdisk -l

Disk /dev/xvda: 8589 MB, 8589934592 bytes, 16777216 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 label type: dos
Disk identifier: 0x000b723c

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *        2048    16777215     8387584   83  Linux

Disk /dev/xvdf: 1073 MB, 1073741824 bytes, 2097152 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    
```

Determine whether we need to create a file system on the volume. New volumes are raw block devices, and we need to create a file system on them before we can mount and use them. Volumes that have been restored from snapshots likely have a file system on them already; if we create a new file system on top of an existing file system, the operation overwrites our data. Use the file -s command to list special information, such as file system type.
```
$ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   8G  0 disk 
└─xvda1 202:1    0   8G  0 part /
xvdf    202:80   0   1G  0 disk 

$ sudo file -s /dev/xvda1
/dev/xvda1: SGI XFS filesystem data (blksz 4096, inosz 512, v2 dirs)

$ sudo file -s /dev/xvda
/dev/xvda: x86 boot sector; partition 1: ID=0x83, active, starthead 32, startsector 2048, 16775168 sectors, code offset 0x63

$ sudo file -s /dev/xvdf
/dev/xvdf: data
```
While the instance volume contains Linux xfs filesystem, the new volume (/dev/xvdf) needs format.

(Conditional) Use the following command to create an xfs file system on the volume. Substitute the device name (such as /dev/xvdf) for device_name. Depending on the requirements of our application or the limitations of our operating system, we can choose a different file system type, such as ext3 or others. List of the file types:

$ sudo fdisk /dev/xvdf
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0xf09e309b.

Command (m for help): l

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris        
 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     85  Linux extended  c7  Syrinx         
 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data    
 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility   
 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt         
 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access     
 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O        
 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor      
 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi eb  BeOS fs        
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         ee  GPT            
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ef  EFI (FAT-12/16/
10  OPUS            55  EZ-Drive        a7  NeXTSTEP        f0  Linux/PA-RISC b
11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f1  SpeedStor      
12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f4  SpeedStor      
14  Hidden FAT16 <3 61  SpeedStor       ab  Darwin boot     f2  DOS secondary  
16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      fb  VMware VMFS    
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE 
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fe  LANstep        
1c  Hidden W95 FAT3 75  PC/IX           be  Solaris boot    ff  BBT            
1e  Hidden W95 FAT1 80  Old Minix      

Command (m for help):

We can also use mkfs[TAB][TAB] what the mkfs can do in terms of file types:

$ mkfs
mkfs         mkfs.btrfs   mkfs.cramfs  mkfs.ext2    mkfs.ext3    mkfs.ext4    mkfs.minix   mkfs.xfs

Caution :
This formatting step assumes that we're mounting an empty volume. If we're mounting a volume that already has data on it (for example, a volume that was restored from a snapshot), don't use mkfs before mounting the volume (skip to the next step instead). Otherwise, we'll format the volume and delete the existing data.

$ sudo mkfs.xfs /dev/xvdf
meta-data=/dev/xvdf              isize=512    agcount=4, agsize=65536 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=262144, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

$ sudo file -s /dev/xvdf
/dev/xvdf: SGI XFS filesystem data (blksz 4096, inosz 512, v2 dirs)

Use the mkdir mount_point command to create a mount point directory for the volume. The mount point is where the volume is located in the file system tree. Substitute a location for mount_point, such as /vol.

$ sudo mkdir /vol

Use the mount command to mount the volume at the location we just created. This will mount the filesystem on /dev/xvdf into the folder /vol. That means that going into /vol will show us the filesystem which is on /dev/xvdf.

$ sudo mount /dev/xvdf /vol

We can check if the xvdf is mounted properly:

$ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   8G  0 disk 
└─xvda1 202:1    0   8G  0 part /
xvdf    202:80   0   1G  0 disk /vol

(Optional I) To mount this Amazon EBS volume on every system reboot, add an entry for the device to the /etc/fstab file.
1. Create a backup of our /etc/fstab file that we can use if we accidentally destroy or delete this file while we are editing it.
2. Open the /etc/fstab file and add a new line to the end of the file for our volume using the following format:
```
device_name  mount_point  file_system_type  fs_mntops  fs_freq  fs_passno  
```
  The last three fields on this line are the file system mount options, the dump frequency of the file system, and the order of file system checks done at boot time. If we don't know what these values should be, then use the values in the example below for them (defaults, nofail 0 2). For more information on /etc/fstab entries, see the fstab manual page (by entering man fstab on the command line). For example, to mount the xfs file system on the device /dev/xvdf at the mount point /vol, add the following entry to /etc/fstab.
  (Note)
  If we ever intend to boot our instance without this volume attached (for example, so this volume could move back and forth between different instances), we should add the nofail mount option that allows the instance to boot even if there are errors in mounting the volume. Debian derivatives, such as Ubuntu, must also add the nobootwait mount option.
```
/dev/xvdf       /vol   xfs    defaults,nofail        0       2
```
3. After we've added the new entry to /etc/fstab, we need to check that our entry works. Run the sudo mount -a command to mount all file systems in /etc/fstab.
4. Let's check out dish using df -h command:
5. To make sure if the volume mount at the boot time, we can check it again after rebooting the instance.

(Optional II) We can run the following script with root privilege (To run a script for the steps #4-8):

#!/bin/bash
mkfs.xfs /dev/xvdf
mkdir /vol
echo "/dev/xvdf /vol auto noatime 0 0" | sudo tee -a /etc/fstab

(Optional III) partition: we can make partitions using fdisk:

Current block device info looks like this:

$ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   8G  0 disk 
└─xvda1 202:1    0   8G  0 part /
xvdf    202:80   0   1G  0 disk

Now, we'll create two partitions that will look like this:

$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda    202:0    0    8G  0 disk 
└─xvda1 202:1    0    8G  0 part /
xvdf    202:80   0    1G  0 disk 
├─xvdf1 202:81   0  399M  0 part 
└─xvdf2 202:82   0   99M  0 part

Before we make partitions, we need to un-mount the volume:

$ umount /vol

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        220M     0  220M   0% /dev
tmpfs           243M     0  243M   0% /dev/shm
tmpfs           243M  8.5M  235M   4% /run
tmpfs           243M     0  243M   0% /sys/fs/cgroup
/dev/xvda1      8.0G  906M  7.2G  12% /
tmpfs            49M     0   49M   0% /run/user/1000

Let's make the partitions:

$ sudo fdisk /dev/xvdf
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p):
Partition number (1-4, default 1): 
First sector (2048-2097151, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-2097151, default 2097151): +399M
Partition 1 of type Linux and of size 399 MiB is set

Command (m for help): p

Disk /dev/xvdf: 1073 MB, 1073741824 bytes, 2097152 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 label type: dos
Disk identifier: 0x7301381b

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdf1            2048      819199      408576   83  Linux

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p):
Partition number (2-4, default 2): 
First sector (819200-2097151, default 819200): 
Using default value 819200
Last sector, +sectors or +size{K,M,G} (819200-2097151, default 2097151): +399M
Partition 2 of type Linux and of size 99 MiB is set

Command (m for help): p

Disk /dev/xvdf: 1073 MB, 1073741824 bytes, 2097152 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 label type: dos
Disk identifier: 0x7301381b

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdf1            2048      819199      408576   83  Linux
/dev/xvdf2          819200     1021951      101376   83  Linux

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

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

Note that the input during the above step means the following:

n: new (create a new one)
p: print current block
w: write

Again, here is our new block info:

$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda    202:0    0    8G  0 disk 
└─xvda1 202:1    0    8G  0 part /
xvdf    202:80   0    1G  0 disk 
├─xvdf1 202:81   0  399M  0 part 
└─xvdf2 202:82   0   99M  0 part