On Sat, Oct 21, 2017 at 01:46:06PM +0200, Lentes, Bernd wrote: > ----- Am 21. Okt 2017 um 4:31 schrieb Duncan 1i5t5.duncan@xxxxxxx: > > Lentes, Bernd posted on Fri, 20 Oct 2017 20:40:15 +0200 as excerpted: > > > >> Is it generally possible to restore a btrfs partition from a tape backup > >> ? > >> I'm just starting, and I'm asking myself. What is about the subvolumes ? > >> This information isn't stored in files, but in the fs ? This is not on a > >> file-based backup on a tape. > > > > Yes it's possible to restore a btrfs partition from tape backup, /if/ you > > backed up the partition itself, not just the files on top of it. Which is usually a quite bad idea: unless you shut down (or remount ro) the filesystem in question, the data _will_ be corrupted, and in the case of btrfs, this kind of corruption tends to be fatal. You also back up all the unused space (trim greatly recommended), and the backup process takes ages as it needs to read everything. An efficient block-level backup of btrfs _would_ be possible as it can nicely enumerate blocks touched since generation X, but AFAIK no one wrote such a program yet. It'd be also corruption free if done in two passes: first a racey copy, fsfreeze(), copy of just newest updates. > > Otherwise, as you deduce, you get the files, but not the snapshot history > > or relationship, nor the subvolumes, which will look to normal file-level > > backup software (that is, backup software not designed with btrfs- > > specifics like subvolumes, which if it did, would likely use btrfs send/ > > receive at least optionally) like normal directories. If the backup software does incrementals well, this is not as bad as it sounds. While rsync takes half an hour just to stat() a typical small piece spinning rust (obviously depending on # of files), that's still in the acceptable range. That backup software can be then be told to back every snapshot in turn. You still lose reflinks between unrelated subvolumes but those tend to be quite rare -- and you can re-dedupe. > i apprehend that i have just a file based backup. We use EMC Networker > (version 8.1 or 8.2), and from what i read in the net i think it does not > support BTRFS. So i have to reinstall, which is maybe not the worst, > because i'm thinking about using SLES 11 SP3. > > What i know now is that i can't rely on our EMC backup. > What would you propose to backup a complete btrfs partition > (https://btrfs.wiki.kernel.org/index.php/Incremental_Backup) ? > We have a NAS with propable enough space, and the servers aren't used > heavily over night. So using one of the mentioned tools in a cronjob over > night is possible. > Which tool do you recommend ? It depends on what you use subvolumes for. While a simple file-base backup may be inadequate for the general case, for most actual uses it works well or at least well enough. Only if you're doing something special, bothering with the complexity might be worth it. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ Laws we want back: Poland, Dz.U. 1921 nr.30 poz.177 (also Dz.U. ⣾⠁⢰⠒⠀⣿⡁ 1920 nr.11 poz.61): Art.2: An official, guilty of accepting a gift ⢿⡄⠘⠷⠚⠋⠀ or another material benefit, or a promise thereof, [in matters ⠈⠳⣄⠀⠀⠀⠀ relevant to duties], shall be punished by death by shooting. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
