-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 2014-12-02 13:23, Greg Freemyer wrote:
On December 2, 2014 5:31:13 AM EST, "Carlos E. R." <> wrote:
On 2014-12-02 07:42, Achim Gratz wrote:
A snapshot is nothing more than telling btrfs "if anything writes to this file, make a copy of it and keep the old data around".
Which is not intuitive: typically a snapshot would be made at the instant of the request, occupying the full needed space. Btrfs snapshots are different, compact and fast. Not a backup snapshot.
I don't find snapshot a well-defined term. There are both COW snapshots and clone snapshots.
I believe most file systems use COW technology to implement snapshots. Linux LVM uses COW.
http://en.m.wikipedia.org/wiki/Snapshot_(computer_storage)#File_systems
But there are also lots of systems that implement snapshots as clones. The way I've seen the most is for a mirror to be created, then broken at snapshot time.
I have seen that mirror method you mention, in unix. Detach one side of the mirror, make a copy elsewhere, reattach the mirror side. I think that xfs implement copy snapshots, to another device or partition. Databases also implement snapshots, which this moment I'm unsure how they are implemented. One way is to flag current records (as in btrfs), copy them to a new file, and during that time, write modifications to new records. When the copy finishes, old records are replaced with the new, and normal operation resumes. Another database I worked with has instead a fixed file, and changes are written to another space (can be ram), which they call "recent changes". So a snapshot can be made by simply copying the file, better after applying the recent changes to the master file. - -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlR9uJIACgkQtTMYHG2NR9WXCACcDefu6xfFOXrcSr4jX1EXVMSX f1kAn3+9UohhgNgL/to5CNBu4Ia9b10T =k2Vy -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse-factory+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-factory+owner@opensuse.org