Overview
CloudStack KVM Overview
How Sendense protects CloudStack KVM environments with SNA, EBA-ST, and the optional snagent host agent.
Overview
CloudStack KVM protection uses SNAs as backup proxies and EBA-ST for data movement. Where supported configured storage is in use, snagent on the hypervisor can improve efficiency by passing extent-map information to the SNA.
Components Involved
Transport Selection
For CloudStack KVM, snagent is used by default when the storage backend configured in SHA for the site or VM is QCOW NFS, ZFS, or LINSTOR DRBD and the host-agent path is available. If the backend is RAW Block, the snagent path is not used.
Host-Assisted Backup Flow
On a supported backend, a host-assisted backup follows this host-side flow:
- snagent prepares a consistent storage-level snapshot of the protected disk on the host, using the mechanism appropriate to the configured backend.
- snagent collects the changed extents for an incremental, or the allocated extents for a full.
- The SNA receives the extent information through QEMU guest tools and reads only the identified extents.
- After the backup completes, snagent cleans up its host-side snapshot and checkpoint state so the host does not accumulate stale artifacts.
Deduplication still applies
The extent map reduces what must be read and sent. Where claims-driven source-side deduplication is active, EBA-ST can also skip blocks the archive already holds; repository deduplication avoids retaining duplicate content.
Fallback Behavior
QCOW NFS, ZFS, and LINSTOR DRBD host-assisted modes require a healthy, correctly placed snagent and can fail if it is unavailable. RAW Block does not use snagent and follows the full-source-read EBA path. Synthetic-incremental storage is not an automatic fallback.
snagent is not required for every Sendense deployment, but it is required for the qualified CloudStack KVM host-assisted modes.
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