I've gone over this in some length in the past. But as with the previous, here are my notes from the session.
- New fstype = shadowfs, provides a linux-level view of a shadow filesystem. By default, linux doesn't see the unified view. Useful for some backup apps, or things like web-servers.
- File-systems participating in DST need to be in the same file-system on the OES server. Could be NFS mounted, might possibly be NCP-mounted in the future. Not yet.
- Migration policy can be set by user.
- Migrations are batched, not done on-demand.
- Can be used to silently migrate a volume to new hardware
- Set new volume as Primary, and old as Shadow
- As users hit data, it gets migrated to Primary from Shadow during nightly migrations.
- Over time, most of a file-system can be migrated this way.
- Directory quotas do NOT replicate over shadow. The shadow quota may be different than Primary quota, and directory quotas are NOT shadow-aware. This is because directory quotas are a function of the file-system, and DST is a function of NCPserv and the client.