docs(features): Add snapshot format and disk usage reference

Signed-off-by: Jerome Jaggi <[email protected]>

Author: JeromeJaggi

pages/features/snapshots.mdx

@@ -48,7 +48,48 @@ ensuring statefulness across different scale-to-zero and scale-to-one cycles,
 but also eliminating any long initialization times from heavyweight apps.
 
 
-## Learn More
+## Snapshot format
+
+When Unikraft Cloud snapshots an instance, it saves the full VM state: CPU registers, device state, and memory contents.
+
+Each snapshot consists of two files:
+
+- **State file** — Device state (CPU registers, device model state).
+- **Memory file** — Memory contents in a compressed format.
+
+The snapshot format uses LZ4 compression and zero-page deduplication to minimize disk usage.
+On-disk snapshot size depends on the amount of memory the app has actually touched, not the total memory allocation.
+
+### Block types
+
+The memory file stores data in blocks.
+Each block has a type that determines how Unikraft Cloud stores it:
+
+| Type | Storage |
+|------|---------|
+| Zero | Not stored on disk — the block contains only zeros. |
+| Raw | Full uncompressed block. |
+| LZ4 | LZ4-compressed block. Only the compressed payload is stored. |
+| Initrd | References the external initrd file. Not stored inline in the snapshot. |
+| Kernel | References the external kernel image. Not stored inline in the snapshot. |
+
+### Disk usage
+
+Zero blocks and reference blocks (initrd, kernel) consume no additional disk space in the snapshot.
+Raw blocks store the full block contents.
+LZ4 blocks store only the compressed payload.
+
+Workloads that touch less memory produce smaller snapshots.
+An app that allocates 256 MiB but only writes to 32 MiB of memory produces a snapshot close to 32 MiB (before compression).
+
+### Restore performance
+
+Unikraft Cloud loads memory pages on demand from the snapshot during restore.
+Restore time is constant (a few milliseconds) regardless of memory size.
+The platform prefetches pages around the first access to reduce page faults during early execution.
+
+## Learn more
 
 * The `kraft cloud` [command-line tool reference](/cli/), and in particular the `deploy` and `instance` subcommands.
 * Unikraft Cloud's [REST API reference](/api/platform/v1), and in particular the [scale-to-zero schema](/api/platform/v1/~schemas#instance-scale-to-zero).
+* [Instance templates](/features/templates) — Templates use snapshots as their base.