Re: rollback to a snapshot

[Roman Mamedov <rm@romanrm.net>]

On Wed, 7 Jun 2023 20:14:27 +0000
Bernd Lentes <bernd.lentes@helmholtz-muenchen.de> wrote:

> I didn't know "--reflink". The help says:
> " When --reflink[=always] is specified, perform a lightweight copy, where the
> data blocks are copied only when modified.  If this is not possible the copy
> fails, or if --reflink=auto is specified, fall back to a standard copy.
> Use --reflink=never to ensure a standard copy is performed.".
> 
> Is that independent from the fs ? That seems to be a kind of a snapshot.
> Am i right ?

Not all filesystems support reflinks.

Btrfs and XFS support it, but for XFS this has to be enabled at FS creation
time (IIRC recent mkfs enables it by default). Ext4, ReiserFS and JFS do not.

For XFS it is a way to have the best of the both worlds: have a filesystem
that is well regarded for performance, but also gain a degree of the CoW
ability that Btrfs is liked for, e.g. allowing instant snapshots of VM images,
including running ones with a point-in-time full image consistency --
unthinkable with traditional copying.

-- 
With respect,
Roman