From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f45.google.com ([74.125.82.45]:52199 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753212AbdKALbs (ORCPT ); Wed, 1 Nov 2017 07:31:48 -0400 Received: by mail-wm0-f45.google.com with SMTP id b9so4335742wmh.0 for ; Wed, 01 Nov 2017 04:31:47 -0700 (PDT) Message-ID: <1509535904.1662.93.camel@gmail.com> Subject: Re: Reasonable amount of snapshots From: ST To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org Date: Wed, 01 Nov 2017 13:31:44 +0200 In-Reply-To: References: <1509534294.1662.91.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, 2017-11-01 at 19:17 +0800, Qu Wenruo wrote: > > On 2017年11月01日 19:04, ST wrote: > > Hello, > > > > I read in different places that one should keep amount of snapshots low > > - around 15-20. My question - is this limitation on total number of > > snapshots on the system or only on related (parent<->child) chain of > > snapshots? > > Independent subvolume doesn't count, and it's filesystem based. > > So only snapshots (with source exists, and still shares a lot of trees > with source) counts. > > And if you have multiple btrfs fses, then the count should be based on > each fs. > > > What I want to do is the following: create (and then rotate) last 7 > > daily snapshots (and maybe 4 weekly) for each user in his /home dir. > > For > > around 100 users. So if limitation is only on related snapshots then I'm > > OK since only each 7 (or maybe 7+4) of them are related which is well > > under the 15-20 limit. However in total there could be 700 snapshots. So > > what is true? > > You're OK since independent subvolumes won't cause too much stress for > backref walk. > > The only thing you may need to consider is to limit the ability to > reflink data between subvolumes. > Like cp --reflink or even offline dedupe. Thank you very much! How can I limit this ability? (I'm on Debian9) All the best!