When the Central Management System appliance is the default DTI source for managed appliances, it downloads software updates from the DTI network on behalf of the appliances. The software updates are temporarily stored in a DTI cache on the Central Management System appliance.
When the Central Management System appliance receives an update request from a managed appliance or makes an update request on behalf of the appliance, the Central Management System appliance first determines whether the requested software is already in the cache and whether it is the latest version. If the requested software is not in the cache, or if the software is out-of-date, the Central Management System appliance downloads the latest software from the DTI network. After the software is in the cache, it is available to update the appliances, as described in Updating Managed Appliances .
You can explicitly download system images and guest images from the DTI network and store them in the cache, even if no appliance requested it. This saves bandwidth and shortens the maintenance window for appliance updates. It also allows you to be more flexible about scheduling appliance updates, because the software is already downloaded and ready to push to the appliances. This can be especially useful for guest images, which can take hours to download. For details, see Downloading Software Updates to the DTI Cache .
To save space on the hard disk, the Central Management System appliance continuously removes out-of-date security content, and removes out-of-date system images and guest images as they are replaced. You can also manually remove security content, guest images, and system images from the cache.
The Central Management System appliance provides the following information about the cache contents.
Size. The size of the guest image, system image, or security content, in bytes.
Type. The type of content:
SysImage—Appliance system image.
GI—Guest image.
GI-Delta—A file containing the changes between a particular version of the guest images and the latest version.
GI-Metadata—A list of the names and versions of the guest images that are available for the managed appliances.
SC-Full—Security content (stored for three hours).
SC-Delta—A file containing the changes between a particular version of the security content and the latest version. Security content is updated every hour (by default), and stale files are automatically removed from the cache.
State. Fresh or Stale. If a system image or guest image has been in the cache longer than 90 days, or if security content has been in the cache longer than three hours for SC-Full or one hour for SC-Delta, it is marked stale. Otherwise, it is marked fresh.
Note
If a system image or guest image is the latest available version, but is older than 90 days, it is still marked stale.
File. The name of the system image guest image, delta, metadata, or security content file. For example,
image-emps_7.7.0.img,win7-sp1.15.0826.img,sc-stable_114.150.img.Last Modification Time. The date and time the file finished downloading from the DTI network to the cache.
Max-Age. The amount of time the content is in the cache before it is marked stale. System images and guest images become stale after 7776000 seconds (90 days). Security content becomes stale after 10800 seconds (3 hours).
Etag. An internal identifier.
Active Download ID. An internal identifier that is displayed when you view the status of the download.
For details about viewing the cache contents, removing software from the cache and other cache management tasks, see Viewing the cache configuration .
Note
This information pertains to a Central Management System appliance running in online mode, in which the cache is always running. The cache is disabled on a Central Management System appliance running in offline mode. For information about how the Central Management System appliance handles software updates for managed appliances when it is in offline mode, see the DTI Offline Portal User's Guide.
Note
The cache is disabled for cloud Central Management System models CM 2500V and CM 4500V. Appliances managed by these models download software updates directly from the DTI network.