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Adding TRIM support to OpenStack Glance images

What is TRIM Support?​

TRIM support is the ability of the virtualization software to pass the TRIM command from the guest operating system to the underlying physical storage device. The TRIM command is used to inform the storage device which blocks of data are no longer in use and can be safely erased, allowing the device to maintain optimal performance over time.

Without TRIM support, the storage device would not know which blocks are free and which are still in use by the guest operating system. As a result, the device may not be able to efficiently manage the available storage space, leading to decreased performance over time.

Enable TRIM in VMs using fstrim​

Note that to fully benefit from TRIM, it needs to be configured both in the Glance image using metadata as well as in your VMs using the SystemD service fstrim. By default, this service runs weekly.

Intro to virtio-scsi​

Virtio-scsi is a virtualization interface that allows virtual machines (VMs) to communicate with storage devices using a SCSI protocol. One of the main benefits of using virtio-scsi in a virtual environment is its support for the TRIM command, which can help to improve the performance and longevity of solid-state drives (SSDs) used as storage devices for VMs.

How to add TRIM support to OpenStack Glance​

Required Image Metadata​

The following metadata is required for the Glance image in order to provide TRIM support

hw_scsi_model=virtio-scsi​

This enables the use of VirtIO SCSI (virtio-scsi) to provide block device access for compute instances; by default, instances use VirtIO Block (virtio-blk). VirtIO SCSI is a para-virtualized SCSI controller device that provides improved scalability and performance, and supports advanced SCSI hardware.

hw_disk_bus=scsi​

This specifies the type of disk controller to attach disk devices to. In our case we want to utilize **scsi** for TRIM support.

Creating an image with fstrim support​

Using the OpenStack CLI​

# Create image with required properties
$ openstack image create --file <PATH_TO_FILE> \
                         --disk-format qcow2 \
                         --container-format bare \
                         --public \
                         --property hw_qemu_guest_agent=yes \
                         --property hw_scsi_model=virtio-scsi \
                         --property hw_disk_bus=scsi \
                         "Trim_Image"

# (Optional) Set distro/version/arch
$ openstack image set "Trim_Image" \
                      --os-distro <DISTRO> \
                      --os-version <VERSION> \
                      --architecture <ARCH> \

Via Horizon (Web GUI)​

When creating a new image within the Horizon web interface, simply select the Metadata tab and under “libvirt Driver Options for Images” and select the “+” next to “Disk Bus” and “SCSI Model”

create-image-metadata.jpg

Adding fstrim support to an existing image​

Via the OpenStack CLI​

openstack image set <IMAGE_NAME_OR_UUID> \
                    --property hw_scsi_model=virtio-scsi \
                    --property hw_disk_bus=scsi

Using Horizon (Web GUI)​

First, select the drop down on the image you want to modify then select “Update Metadata”

select-update-metadata.jpg

Next, on the left hand tab under “libvirt Driver Options for Images” and select the “+” next to “Disk Bus” and “SCSI Model”

update-image-metadata.jpg