From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Nicol Subject: Re: Can you please define "snapshot" and "subvolume"? Date: Thu, 7 Oct 2010 15:48:42 -0500 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: linux-btrfs To: Francis Galiegue Return-path: In-Reply-To: List-ID: On Thu, Oct 7, 2010 at 6:39 AM, Francis Galiegue wrote: > While I fully understand (and use) the purpose of snapshots, I don't > quite fathom the use case for subvolumes, apart from btrfs-convert... > Why has btrfs grown such a feature in the first place? Can someone > give me a use case for them? I'm new here; I trust that someone will correct me if wrong: As I understand it, since snapshotting works on volumes, having subvolumes allows a smaller thing that you can take a snapshot of. A use case? One could give each user on a multi-user system their own subvolume rather than their own directory, under /home/... and then take snapshots of these home directories to implement regular backups (1)without duplicating unchanged files and (2) with independence between the users. As to why they exist, I understand that they began as an implementation detail of snapshots, rather than their creation having been driven by the needs of a particular use case, and one could legitimately criticize currently offered use cases (such as the one above) as contrived. I believe it is fair to consider a new subvolume as equivalent of a snapshot of an empty file system.