InfoScale™ 9.0 Virtualization Guide - Linux
- Section I. Overview of InfoScale solutions used in Linux virtualization
- Overview of supported products and technologies
- About InfoScale support for Linux virtualization environments
- About KVM technology
- About InfoScale deployments in OpenShift Virtualization environments
- Overview of supported products and technologies
- Section II. Implementing a basic KVM environment
- Getting started with basic KVM
- InfoScale solutions configuration options for the kernel-based virtual machines environment
- Installing and configuring VCS in a kernel-based virtual machine (KVM) environment
- Configuring KVM resources
- Getting started with basic KVM
- Section III. Implementing InfoScale an OpenStack environment
- Section IV. Implementing Linux virtualization use cases
- Application visibility and device discovery
- Server consolidation
- Physical to virtual migration
- Simplified management
- Application availability using Cluster Server
- Virtual machine availability
- Virtual machine availability for live migration
- Virtual to virtual clustering in a Hyper-V environment
- Virtual to virtual clustering in an OVM environment
- Multi-tier business service support
- Managing Docker containers with InfoScale Enterprise
- About the Cluster Server agents for Docker, Docker Daemon, and Docker Container
- Managing storage capacity for Docker containers
- Offline migration of Docker containers
- Disaster recovery of volumes and file systems in Docker environments
- Section V. Reference
- Appendix A. Troubleshooting
- Appendix B. Sample configurations
- Appendix C. Where to find more information
- Appendix A. Troubleshooting
VirtIO disk drives
VirtIO is an abstraction layer for paravirtualized hypervisors in Kernel-based Virtual Machine (KVM) technology. Unlike full virtualization, VirtIO requires special paravirtualized drivers running in each VM guest. VirtIO provides support for many devices including network devices and block (disk) devices. Using VirtIO to export block devices to a host allows files, VxVM volumes, DMP meta-nodes, SCSI devices or any other type of block device residing on the host to be presented to the VM guest. When SCSI devices are presented to a VM guest using VirtIO, in addition to simple reads and writes, SCSI commands such as SCSI inquiry commands can be performed, which allows VxVM in the guest to perform deep device discovery. Running VxVM and DMP on the host and on the VM guest provides for consistent naming of SCSI devices from the array to the host through to the VM guest.
InfoScale 9.0 supports VirtIO SCSI devices and VirtIO block devices with Linux KVM. virtio-scsi
is a virtual SCSI HBA interface, which is the foundation of an alternative storage implementation for virtual machines. It replaces virtio-blk
on Red Hat Enterprise Linux (RHEL) with improved scalability and provides standard SCSI command set support.
The VirtIO feature that is used in the context of InfoScale is dynamically adding devices. VirtIO disk devices can be both, added and removed, from a running VM guest dynamically, without the need for a reboot.
The VirtIO limitations in the context of InfoScale are:
Disk caching:
When disks are exported to the VM guest with the cache enabled, the VxVM configuration changes may get cached on the KVM host and may not be applied to the disks. When disks are shared between more than one VM guest, such a configuration change is not visible from VM guests other than the one on which the change was made. To avoid potential configuration conflict, disable caching the host (cache=no) while exporting the disks.
SCSI commands:
SCSI devices that are presented as VirtIO devices to a VM guest support a limited subset of the SCSI command set. The KVM hypervisor blocks the restricted commands.
DMP Fast Recovery with SCSI devices:
DMP Fast Recovery bypasses the normal VirtIO read/write mechanism, performing SCSI commands directly against the device. If DMP Fast Recovery is used within the VM guest, caching in the host must be disabled (cache=none) to avoid data integrity issues.
Thin reclamation:
Thin reclamation is not supported on VirtIO devices. The WRITE-SAME command is blocked by the hypervisor. This limitation may be removed in future releases of Linux.
Resizing devices:
Linux does not support online disk resizing of VirtIO devices. To resize a VirtIO device, the VM guest must be fully shut down and restarted. Support for online resizing of block devices is under evaluation for Linux.
Maximum number of devices:
You can use
virtio-scsi
to configure disk devices inside the KVM guest. For details on the maximum number of devices that can be used, refer to the KVM documentation.VxFS known issue:
In a KVM environment under heavy I/O load, data corruption may occur on VxFS file systems that are created on LUNs attached as VirtIO block devices. For details, refer to Case # 00945974 on the Red Hat Support site.