Move application data to a data disk - Elastic Compute Service

Transfer business data from a system disk directory to a data disk to reduce system disk load on a Linux ECS instance.

Warning

Data migration may disrupt your business. Consider resizing the system disk instead. See Step 1: Resize a disk to extend the disk capacity.

Prerequisites

The system disk usage is below 100%.

Important
Log on to the instance and run df -h to check root partition usage. If usage reaches 100%, see Resolve "no space left" issues on Linux.
The target data disk meets the following requirements:
- The data disk is in the In Use (In_use) state.
- The data disk is initialized with no file system mounted. See Initialize a data disk on a Linux instance.

The following example transfers data from the /userdata directory to the /dev/vdb1 partition on Alibaba Cloud Linux 3.2104. Replace /userdata and /dev/vdb1 with your actual directory and partition names.

Workflow

Procedure

Step 1: Back up the system disk

Create a snapshot of the system disk to prevent data loss. See Create snapshot manually.

Note

Snapshots incur fees. See Snapshot billing.

Step 2: Copy data to the data disk

Create the /temporary directory and mount the data disk partition. Replace /dev/vdb1 with your actual partition name.
```
sudo mkdir /temporary
sudo mount /dev/vdb1 /temporary
```
Copy data from /userdata to the mounted /temporary directory. Replace /userdata with your actual directory name.
```
sudo cp -rv /userdata/. /temporary
```
Alternatively, use rsync to copy files with progress display.
```
sudo yum install -y rsync
rsync --progress /userdata/* /temporary
```

Step 3: Mount the data disk partition to the data directory

Unmount the /temporary directory.
```
sudo umount /temporary
```
Rename /userdata to /userdata_bak as a short-term backup.
```
sudo mv /userdata /userdata_bak
```
Warning
Renaming the data directory may cause business errors and short-term data loss. Evaluate the risks and perform this operation during off-peak hours.
Rename /temporary to /userdata. Replace /userdata with your actual directory name.
```
sudo mv /temporary /userdata
```
Mount /dev/vdb1 to /userdata. Replace with your actual partition and directory names.
```
sudo mount /dev/vdb1 /userdata
```

Run the df -Th command to check if the data disk partition is mounted to the target directory. The following output shows that /dev/vdb1 is mounted to /userdata.

[ecs-xxx                              ~]$ df -Th
Filesystem     Type      Size  Used Avail Use% Mounted on
devtmpfs       devtmpfs  867M     0  867M   0% /dev
tmpfs          tmpfs     879M     0  879M   0% /dev/shm
tmpfs          tmpfs     879M  436K  878M   1% /run
tmpfs          tmpfs     879M     0  879M   0% /sys/fs/cgroup
/dev/vda1      ext4       40G  2.8G   35G   8% /
/dev/vdb1      ext4       40G  3.8G   34G  11% /userdata

Step 4: Verify business system operation

Restart the business system and verify that it runs as expected.
If an issue occurs, restore the business system:
- Solution 1: Reverse the directory changes from Step 3.
  Unmount /userdata.
  
  Rename /userdata to /temporary.
  
  Rename /userdata_bak back to /userdata.
  
  Restart the business system.
- Solution 2: Roll back the system disk with a snapshot. See Roll back disk using snapshot.
After confirming the business system runs normally, delete the /userdata_bak directory.