Some scenarios require virtual environments to be migrated, such as those in which Xen Project versions reach their end of life (EOL), Elastic Compute Service (ECS) instances need to be migrated because the warranty of their hosts expire, or ECS instances need to be migrated from the classic network to a virtual private cloud (VPC). In such scenarios, after ECS instances are migrated, some of the instances may experience a kernel panic error, a blue screen error, or an INACCESSIBLE_BOOT_DEVICE error. The INACCESSIBLE_BOOT_DEVICE error indicates that the system is unable to access the boot device. This topic describes how to resolve these issues.
Background information
Alibaba Cloud ECS provides a wide array of instance families and images that contain mainstream operating systems. For more information, see Overview of instance families and Overview of public images. Different ECS instance types are based on different virtualization technologies. Examples:
The retired ecs.t1 and ecs.s1 instance families are based on Xen virtualization technology and require images to contain specific drivers such as Xen drivers.
The ecs.g5 instance family is based on Kernel-based Virtual Machine (KVM) virtualization technology and requires images to contain the virtio driver.
The ecs.g7 instance family is based on SHENLONG architecture and requires images to contain the virtio driver.
The preceding drivers are provided by image kernels. The instance types supported by the drivers vary based on kernel versions. By default, the kernels of specific early operating system versions do not contain these drivers. For these operating system versions, you must manually install the drivers. The drivers in the kernels of early operating system versions may be incompatible with later-generation instance types.
Precautions for migration
If an instance that you want to migrate from Xen to KVM encounters a system environment exception, the instance may be unable to run as expected after it is migrated. For example, the registry or file systems of the instance may be damaged, or the instance may be unable to start. To ensure that an instance can be migrated and run as expected after the migration, we recommend that you make preparations before you migrate the instance.
Before you migrate the instance, we recommend that you restart the instance to ensure that the instance can start and that the instance and the business hosted on it are normal.
Before you migrate the instance, we recommend that you create snapshots for the instance to back up data. For more information, see Create a snapshot for a disk.
In addition to existing migration solutions, you can also use custom images to migrate instances from Xen to KVM. You can create custom images from the instances that you want to migrate and then use the custom images to create instances of KVM-based instance types. For more information, see Create a custom image from an instance and Create an ECS instance by using a custom image.
A SHENLONG environment is incompatible with an early operating system version
SHENLONG environments are incompatible with the following early operating system versions:
Windows Server 2003 and earlier. Windows Server 2008 Standard supports SHENLONG environments on the premise that Xen registry information is cleared.
CentOS 5.8 and earlier and Red Hat 5.8 and earlier, including other CentOS and Red Hat versions that are based on the CentOS 5 or Red Hat 5 kernel 2.6.18-348 or earlier.
Debian versions earlier than 6.09. Debian versions earlier than 6.09 may be incompatible with KVM. We recommend that you upgrade to Debian 6.09 or later.
FreeBSD versions earlier than 11. For FreeBSD 11 and 12, install patches provided by Alibaba Cloud. For more information, see FAQ about images in use of ECS instances .
Ubuntu 10 and earlier. Ubuntu 12 can start based on kernel 3.2. No public images that contain Ubuntu versions earlier than 12 have ever been provided by Alibaba Cloud.
SUSE Linux Enterprise Server 10 and earlier. No public images that contain SUSE Linux Enterprise Server versions earlier than 11 have been provided by Alibaba Cloud.
openSUSE versions earlier than 13. No public images that contain openSUSE versions earlier than 13 have been provided by Alibaba Cloud.
Gentoo. The Gentoo operating systems provided by Alibaba Cloud support only Xen. If you want the Gentoo operating systems to support KVM, we recommend that you upgrade to the most recent Gentoo version. Alibaba Cloud have not provided Gentoo operating systems since 2016.
The preceding operating system versions are incompatible with SHENLONG environments for 6th-generation instance types. Instance types of the 7th or later generations have more compatibility constraints.
Solution 1: Upgrade the operating system by replacing the system disk
The preceding early operating system versions reached end of maintenance (EOM) and end of update long ago. For more information, see Maintenance support for operating systems. Operating system versions that reached EOM and end of update are vulnerable to a variety of issues such as functionality risks, security risks, and system vulnerabilities that cannot be fixed. We recommend that you upgrade your operating systems as soon as possible.
Alibaba Cloud provides public images for mainstream Linux distributions and Windows versions. For more information, see Overview of public images.
You can upgrade the operating system of an instance by replacing the instance system disk with a few clicks. For more information, see Replace the operating system (system disk) of an instance.
Copy data from the original system disk.
If you want to copy data from the original system disk, you can detach the system disk and retain it as a data disk. For more information, see Detach or attach a system disk.
Migrate services and applications from the original system disk.
Deploy the services that were deployed on the original system disk to the new system disk.
Migrate applications such as databases from the original system disk to the new system disk. For more information, see Overview.
This solution has the following benefits and drawbacks:
Benefits: This solution is easy to use. You can select an appropriate image from a wide variety of Alibaba Cloud public images and switch to a more recent operating system version by replacing the instance system disk.
Drawbacks: You must back up data from the original system disk and redeploy some applications and services to the new system disk.
Solution 2: Upgrade to the most recent minor release of the current operating system version
You can upgrade the operating system of your instance to the most recent minor release. For example, you can upgrade CentOS 5 to CentOS 5.11. For more information, see the following topics:
This solution has the following benefits and drawbacks:
Benefits: The upgrade does not affect the data and services in the original operating system.
Drawbacks: If you upgrade your instance operating system (such as CentOS 5) to a more recent minor release (such as CentOS 5.11) that is no longer maintained and updated, vulnerabilities and risks remain in the operating system and you have no access on the instance to the new features provided by more recent operating system versions (such as CentOS 7 and 8).
Solution 3: Use an earlier-generation instance type
You can use a 5th-generation instance type that is not based on SHENLONG environments. Example: an ecs.n, ecs.xn, or ecs.c5 instance type. For more information, see Overview of instance families.
The virtio driver failed to be installed or configured
After an instance is migrated from Xen to KVM, if the virtio driver fails to be installed or configured on the instance, the instance experiences downtime or a blue screen error. Possible causes:
The virtio driver is not installed or configured on Linux.
The driver failed to be installed on instance startup.
The Windows registry is damaged.
Security software such as 360 is installed on Windows.
Solutions
For a Linux instance, if the Linux kernel is damaged, download and install the official Linux kernel and try again.
For a Windows instance, contact Alibaba Cloud technical support to attach the system disk of the instance to the PE system by using Winpe 3.0 ISO and use built-in tools to repair the virtio driver.
Before you migrate a Windows instance, we recommend that you use the System File Checker to verify system integrity (including registry integrity) and uninstall security software such as 360.