Alternative to NFS: Image on Local Disk
Intended for use with Cassatt Active Response V5.0.
Cassatt Active Response relies on NFS for booting images for nodes in tiers. If your site policies discourage using NFS, you can configure Cassatt Active Response to boot a node's image from local disk. This alternative is most effective if the node is stateless, if you don't need to retain data on local disk, or if you have a sufficient backup strategy.
How image on local disk works
When a node gets its image from local disk, all data on the image instance is copied to the local disk when the tier is activated. After this point, there is no flow or synchronization back to the image instance. This means if a node fails or the disk fails, any locally stored data is lost unless you still have access to the machine, or you have a backup.
Tier activation can take longer to boot the first time because Cassatt Active Response is pushing down all of the bits to that node; subsequent boots in the tier happen at the normal rate. Also, when a tier is first activated, Cassatt Active Response will boot nodes in groups of four to limit network traffic.
The image on local disk feature can be selected on an image-by-image basis.
How to configure Cassatt Active Response for image on local disk
Follow these steps to configure Cassatt Active Response for image on local disk:
- Understand operating system limitations; for this release, the image on local disk option is not supported for Windows.
- During cccapture, specify the local disk size, and change the default (No) to 'Yes' to install the image on local disk.
- Enter the minimum size in Gbytes for the required local disk:
- Should this image be installed on the local disk (allowing the node to boot locally)? [n]
- Consider turning off the following tier settings: Automatic Move to Maintenance Pool and Node Harvesting. Why? Data on local disk may be lost when a node is deallocated and subsequently reallocated for use. To turn off this feature, go to: Tiers > tier link > Properties > Automatic Move to Maintenance Pool = Off and Allow Harvest = Off.
- Understand monitoring limitations.
Cassatt Active Response does not allow ping monitoring when using the image on local disk option. This is a problem with ping, which can report nodes as being up before they are ready to be used.
Use script monitoring with caution. Simple script monitors that always return true (for example, /bin/true) should be avoided for the same reasons as ping. Instead, use scripts that faithfully reflect the state of your applications or services running on the node.
How to manage images on local disk
The following table describes how to manage images on local disk in the Controller. Note that basic image operations do not change (create, export, properties), but a few of the details are different.
Task |
Description |
Change image properties |
Images on local disk values are set in: Images > Requirements: Perform local installation and Local Disk (where local disk size is: image size + swap size + estimated expected growth.)
You can select and deselect these values anytime, unless the image has allocated tiers. |
Create a new image |
The easiest way to create an image is to duplicate a regular image, and then follow the steps to configure image on local disk settings. |
Configure image |
No difference. Configuring the image is always done using NFS. |
Delete image |
No difference. |
Export and import images |
No difference. |
Personalize image |
Active tiers using image on local disk cannot be personalized unless the tier is deactivated. All personalization is done using NFS, regardless if image on local disk is configured. |
Update image |
You make updates to the local image instance used to boot the image. Changes are not copied back to the control nodes. After the instance is updated, it is re-installed on the node. |
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