From mboxrd@z Thu Jan 1 00:00:00 1970 From: TARUISI Hiroaki Subject: Re: btrfs-progs: New utility to swap subvolumes Date: Mon, 04 Jan 2010 09:49:44 +0900 Message-ID: <4B413B28.7090604@jp.fujitsu.com> References: <4B32CF4D.90406@jp.fujitsu.com> <200912272123.37585.kreijack@alice.it> <4B380C22.4010809@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Cc: linux-btrfs@vger.kernel.org To: kreijack@gmail.com Return-path: In-Reply-To: <4B380C22.4010809@jp.fujitsu.com> List-ID: Buon anno, Goffredo. Taking snapshot in btrfs is very easy, but handling snapshots is very confusing. So, we must make a rule of snapshotting such as your proposal, which seems to me very good and useful. If rules like this are forced regardless of operator's preference, this utility may become a deadwood. Identification with non-filesystem-related identifier seems to me a good idea. But because subvolume is unique idea in btrfs, identifying subvolumes can be unique, too. Subvolume ID represents some information belong to subvolume (like snapshot date/time... not data which subvolume contains), and not variable. It becomes useful information/identifier to handle snapshots although it's not friendly to human being. Regards, taruisi >Hi Taruisi, > >On Monday 28 December 2009, TARUISI Hiroaki wrote: >[...] > >> We can swap subvolumes regardless of mounted-subvolume. (only >> when we mount other subvolume than fs tree) >I resolved this kind of problem as described in my previous email ([RFC] >proposal for a btrfs filesystem layout - 20/Nov/2009): I used a sub-volume as >root of my system, but I mounted also the root of the btrfs filesystem for >handling the sub-volumes under "/var/btrfs". It work quiet well: >1) I can swap the sub-volumes only with the mv commands >2) I can switch to an old snapshot of the root at boot time, because my >scripts update the grub entries with the list of the valid snapshots >3) I can switch permanently two sub-volumes exchanging their names >4) I can remove a sub-volume quite easily > >> And, because we can identify snapshot (its date or target subvol) >> with subvolume ID, it is suitable to swap with ID. >Why you want to to identify a sub-volume with its id ? >I like the idea to identify a sub-volumes with an identifier which is not >file-system related. To me the fact that a sub-volume is identified with its >"mount point" seems to me a limit instead that an advantage. But it seems that >I am alone to thinking that :-( >So I am curious about your reasons. > >BR >Goffredo > >-- >gpg key@ keyserver.linux.it: Goffredo Baroncelli (ghigo) >Key fingerprint = 4769 7E51 5293 D36C 814E C054 BF04 F161 3DC5 0512