Elastic Compute Service:Restore data on Linux instances

(Optional) Check disk information

Check the current disk information:

sudo fdisk -lu

Sample output:

Disk /dev/vda: 145 GiB, 155692564480 bytes, 304087040 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
Disklabel type: gpt
Disk identifier: F51132A7-xxxx-xxxx-xxxx-FD0DE6E1210C

In this example, the /dev/vda disk is displayed. The Device field is missing, which indicates a corrupted partition table.

Use fdisk to restore partitions

In most cases, partitioning a data disk uses default start and end sectors. Run fdisk to re-create partitions on the data disk.

Run the fdisk /dev/xvdb command to re-create the partition, then mount and verify data recovery:

[root@Aliyun ~]# fdisk /dev/xvdb
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): p
Partition number (1-4, default 1): 1
First sector (2048-10485759, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-10485759, default 10485759):
Using default value 10485759
Partition 1 of type Linux and of size 5 GiB is set

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

Calling ioctl() to re-read partition table.
Syncing disks.
[root@Aliyun ~]# mount /dev/xvd
xvda   xvda1  xvdb   xvdb1
[root@Aliyun ~]# mount /dev/xvdb
xvdb   xvdb1
[root@Aliyun ~]# mount /dev/xvdb1 /mnt/
[root@Aliyun ~]# ls /mnt/
123.sh  configclient  data  diamond  install_edsd.sh  install.sh  ip.qz

If the partition cannot be mounted after running fdisk, or if files are not visible after mounting, use testdisk to restore partitions or use testdisk to restore data.

Use testdisk to restore partitions

This example uses the /dev/xvdb disk. To restore partitions with testdisk, perform the following steps:

1. Install testdisk.

   Alibaba Cloud Linux 3, Alibaba Cloud Linux 2, CentOS 6, CentOS 7, or CentOS 8

   sudo yum install -y testdisk

   Ubuntu or Debian

   sudo apt install -y testdisk

2. Run testdisk /dev/xvdb. Replace /dev/xvdb with your data disk device name. Select Proceed (default) and press Enter.

   TestDisk 7.0, Data Recovery Utility, April 2015
   Christophe GRENIER <grenier@cgsecurity.org>
   http://www.cgsecurity.org
   
     TestDisk is free software, and
     comes with ABSOLUTELY NO WARRANTY.
   
   Select a media (use Arrow keys, then press Enter):
   >Disk /dev/xvdb - 5368 MB / 5120 MiB
   
   >[Proceed ]  [  Quit  ]
   
   Note: Disk capacity must be correctly detected for a successful recovery.
   If a disk listed above has incorrect size, check HD jumper settings, BIOS
   detection, and install the latest OS patches and disk drivers.

3. Select the partition table style. The default is Intel. For GPT disks, select EFI GPT.

   TestDisk 7.0, Data Recovery Utility, April 2015
   Christophe GRENIER <grenier@cgsecurity.org>
   http://www.cgsecurity.org
   
   Disk /dev/xvdb - 5368 MB / 5120 MiB
   
   Please select the partition table type, press Enter when done.
   >[Intel  ]  Intel/PC partition
    [EFI GPT]  EFI GPT partition map (Mac i386, some x86_64...)
    [Humax  ]  Humax partition table
    [Mac    ]  Apple partition map
    [None   ]  Non partitioned media
    [Sun    ]  Sun Solaris partition
    [XBox   ]  XBox partition
    [Return ]  Return to disk selection
   
   Note: Do NOT select 'None' for media with only a single partition. It's very
   rare for a disk to be 'Non-partitioned'.

4. Select Analyse and press Enter.

   Disk /dev/xvdb - 5368 MB / 5120 MiB
        CHS 652 255 63 - sector size=512
   
   [ Analyse  ] Analyse current partition structure and search for lost partitions
   [ Advanced ] Filesystem Utils
   [ Geometry ] Change disk geometry
   [ Options  ] Modify options
   [ MBR Code ] Write TestDisk MBR code to first sector
   [ Delete   ] Delete all data in the partition table
   [ Quit     ] Return to disk selection
   
   Note: Correct disk geometry is required for a successful recovery. 'Analyse'
   process may give some warnings if it thinks the logical geometry is mismatched.

5. If no partition information is displayed, select Quick Search and press Enter.

   Disk /dev/xvdb - 5368 MB / 5120 MiB - CHS 652 255 63
   Current partition structure:
        Partition                  Start        End    Size in sectors
   
   No partition is bootable
   
   *=Primary bootable  P=Primary  L=Logical  E=Extended  D=Deleted
   >[Quick Search]
                           Try to locate partition

   After the Quick Search completes, the found Linux partition is displayed (marked as Primary bootable, size 10483712 sectors), and the Structure status shows Ok.

   Disk /dev/xvdb - 5368 MB / 5120 MiB - CHS 652 255 63
        Partition                  Start        End    Size in sectors
   >* Linux                    0  32 33    652 180 40    10483712
   
   Structure: Ok.  Use Up/Down Arrow keys to select partition.
   Use Left/Right Arrow keys to CHANGE partition characteristics:
   *=Primary bootable  P=Primary  L=Logical  E=Extended  D=Deleted
   Keys A: add partition, L: load backup, T: change type, P: list files,
        Enter: to continue

6. Select a partition and press Enter.

7. Select Write to save the partition.

   Note

   If the expected partition is not listed, select Deeper Search to continue searching.

   After confirming the partition information is correct, select Write to write the partition structure to the disk.

   Disk /dev/xvdb - 5368 MB / 5120 MiB - CHS 652 255 63
   
        Partition                  Start        End    Size in sectors
   
    1 * Linux                  0  32 33   652 180 40    10483712
   
   
   [ Quit ]  [Deeper Search]  [> Write  ]
                   Write partition structure to disk

8. Press Y to save the partition.

   TestDisk 7.0, Data Recovery Utility, April 2015
   Christophe GRENIER <grenier@cgsecurity.org>
   http://www.cgsecurity.org
   
   write partition table, confirm ? (Y/N)

9. Run partprobe /dev/xvdb to refresh the partition table. Replace /dev/xvdb with your data disk device name.

10. Remount the partition and verify the data.

    The ip.qz file in the output is the recovered target file.

    [root@Aliyun home]# mount /dev/xvdb1 /mnt/
    [root@Aliyun home]# ls /mnt/
    123.sh  configclient  data  diamond  install_edsd.sh  install.sh  ip.qz  logs  lost+found  test

Common misunderstandings

Alibaba Cloud uses triplicate storage, which leads some users to assume no data loss risk exists. However, triplicate storage only protects data at the physical layer. Logical issues such as viruses, accidental deletions, or file system corruption can still cause data loss. Use snapshots and geo-redundancy to improve data security. See ESSD cloud disk data reliability.

Best practices

Partition and data restoration may not always succeed. Follow these best practices to maximize data security with snapshots and backups.

• Apply automatic snapshot policies

  Apply automatic snapshot policies to system disks or data disks.

  Important

  When a system disk is replaced, an instance expires, or a disk is manually released, associated automatic snapshots may be released. To release automatic snapshots along with the disk, select Delete Automatic Snapshots While Releasing Disk in the Modify Attributes dialog box in the ECS console. To retain them, clear this option. See Snapshot FAQ and Create an automatic snapshot policy.

• Create manual snapshots

  Create manual snapshots before the following high-risk operations:

  • Update the kernel.

  • Upgrade or change applications.

  • Restore data on disks.

  Always create a snapshot before restoring a disk. Proceed with restoration only after the snapshot completes.

• OSS backup, offline backup, and geo-redundancy

  Back up important data with OSS, offline backup, or geo-redundancy based on your business requirements.