-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 04/07/14 21:38, Goffredo Baroncelli wrote: > On 07/04/2014 04:38 PM, Bob Williams wrote: >> I have a disc formatted as btrfs, on which is mounted /home. >> >> /home/bob is a regular directory. >> >> /home/bob/Documents is a btrfs subvolume >> >> /home is btrfs root >> >> If I do >> >> # mv /home/bob /home/bob_original # btrfs subvolume create >> /home/bob # mv /home/bob_original/* /home/bob/ # rm >> /home/bob_original >> >> will the original subvolume /home/bob/Documents survive this >> operation, and will it now exist as a subvolume under the new >> subvolume /home/bob? > > Yes. > > A subvolume is a way to partition a btrfs file-system. You can > think a subvolume like a filesystem. For objects like files and > directory a move command between *different* subvolumes is equal to > a copy+remove. If fact is like you are moving data between > different file-systems. > > Instead moving a subvolume in *its btrfs filesystem* is a cheap > operation (is like moving a link); this is true even if you move a > subvolume between different subvolumes. > > To increase the speed when you move files between subvolumes (of > the *same* btrfs filesystem), you could do a "cp --reflink" + "rm" > instead of a "mv"; eg > > # mv subvolume-A/* subvolume-B/ > > is equal to > > # cp -rf subvolume-A/* subvolume-B/ # rm -rf subvolume-A/* > > but # cp --reflink -R subvolume-A/* subvolume-B/ # rm -rf > subvolume-A/ > > is faster because "cp --reflink" shared the data between source > and destination. This means that you are doing a copy (and a > delete) of metadata only. > > Thank you, Goffredo. As the current /home/bob is not a subvolume, but a regular linux directory/folder, will the "cp --reflink" still carry the same speed advantage? In other words, using your example above, will this work: # cp --reflink -R normal_directory-A/* subvolume-B/ # rm -rf normal_directory-A/ - -- Bob Williams System: Linux 3.11.10-17-desktop Distro: openSUSE 13.1 (x86_64) with KDE Development Platform: 4.13.2 Uptime: 06:00am up 5 days 20:14, 3 users, load average: 0.00, 0.04, 0.08 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlO3F24ACgkQ0Sr7eZJrmU5UaACfcxJObM9sEzaRIoDGBhXCsWXz lb4An3OwTzXu/l4r/IhT1u+DbLcVPg3h =S0Hg -----END PGP SIGNATURE----- -- 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
