Re: Are nocow files snapshot-aware

2014-02-08 Thread Kai Krakow
Duncan 1i5t5.dun...@cox.net schrieb: [...] Difficult to twist your mind around that but well explained. ;-) A snapshot thus looks much like a crash in terms of NOCOW file integrity since the blocks of a NOCOW file are simply snapshotted in-place, and there's already no checksumming or file

Re: Are nocow files snapshot-aware

2014-02-07 Thread Kai Krakow
Chris Murphy li...@colorremedies.com schrieb: If the database/virtual machine/whatever is crash safe, then the atomic state that a snapshot grabs will be useful. How fast is this state fixed on disk from the time of the snapshot command? Loosely speaking. I'm curious if this is 1 second; a

Re: Are nocow files snapshot-aware

2014-02-07 Thread Chris Murphy
On Feb 7, 2014, at 2:07 PM, Kai Krakow hurikhan77+bt...@gmail.com wrote: Chris Murphy li...@colorremedies.com schrieb: If the database/virtual machine/whatever is crash safe, then the atomic state that a snapshot grabs will be useful. How fast is this state fixed on disk from the time of

Re: Are nocow files snapshot-aware

2014-02-07 Thread Kai Krakow
Duncan 1i5t5.dun...@cox.net schrieb: The question here is: Does it really make sense to create such snapshots of disk images currently online and running a system. They will probably be broken anyway after rollback - or at least I'd not fully trust the contents. VM images should not be

Re: Are nocow files snapshot-aware

2014-02-07 Thread Kai Krakow
Chris Murphy li...@colorremedies.com schrieb: On Feb 7, 2014, at 2:07 PM, Kai Krakow hurikhan77+bt...@gmail.com wrote: Chris Murphy li...@colorremedies.com schrieb: If the database/virtual machine/whatever is crash safe, then the atomic state that a snapshot grabs will be useful. How

Re: Are nocow files snapshot-aware

2014-02-07 Thread Duncan
Kai Krakow posted on Fri, 07 Feb 2014 23:26:34 +0100 as excerpted: So the question is: Do btrfs snapshots give the same guarantees on the filesystem level that write-barriers give on the storage level which exactly those processes rely upon? The cleanest solution would be if processes could

Re: Are nocow files snapshot-aware

2014-02-06 Thread Kai Krakow
Duncan 1i5t5.dun...@cox.net schrieb: Ah okay, that makes it clear. So, actually, in the snapshot the file is still nocow - just for the exception that blocks being written to become unshared and relocated. This may introduce a lot of fragmentation but it won't become worse when rewriting the

Re: Are nocow files snapshot-aware

2014-02-06 Thread cwillu
On Thu, Feb 6, 2014 at 6:32 PM, Kai Krakow hurikhan77+bt...@gmail.com wrote: Duncan 1i5t5.dun...@cox.net schrieb: Ah okay, that makes it clear. So, actually, in the snapshot the file is still nocow - just for the exception that blocks being written to become unshared and relocated. This may

Re: Are nocow files snapshot-aware

2014-02-06 Thread Chris Murphy
On Feb 6, 2014, at 6:01 PM, cwillu cwi...@cwillu.com wrote: On Thu, Feb 6, 2014 at 6:32 PM, Kai Krakow hurikhan77+bt...@gmail.com wrote: Duncan 1i5t5.dun...@cox.net schrieb: Ah okay, that makes it clear. So, actually, in the snapshot the file is still nocow - just for the exception that

Re: Are nocow files snapshot-aware

2014-02-06 Thread Duncan
Kai Krakow posted on Fri, 07 Feb 2014 01:32:27 +0100 as excerpted: Duncan 1i5t5.dun...@cox.net schrieb: That also explains the report of a NOCOW VM-image still triggering the snapshot-aware-defrag-related pathology. It was a _heavily_ auto- snapshotted btrfs (thousands of snapshots,

Re: Are nocow files snapshot-aware

2014-02-05 Thread Kai Krakow
David Sterba dste...@suse.cz schrieb: On Tue, Feb 04, 2014 at 08:22:05PM -0500, Josef Bacik wrote: On 02/04/2014 03:52 PM, Kai Krakow wrote: Hi! I'm curious... The whole snapshot thing on btrfs is based on its COW design. But you can make individual files and directory contents nocow by

Re: Are nocow files snapshot-aware

2014-02-05 Thread Duncan
Kai Krakow posted on Wed, 05 Feb 2014 19:17:10 +0100 as excerpted: David Sterba dste...@suse.cz schrieb: On Tue, Feb 04, 2014 at 08:22:05PM -0500, Josef Bacik wrote: On 02/04/2014 03:52 PM, Kai Krakow wrote: Hi! I'm curious... The whole snapshot thing on btrfs is based on its COW

Are nocow files snapshot-aware

2014-02-04 Thread Kai Krakow
Hi! I'm curious... The whole snapshot thing on btrfs is based on its COW design. But you can make individual files and directory contents nocow by applying the C attribute on it using chattr. This is usually recommended for database files and VM images. So far, so good... But what happens to

Re: Are nocow files snapshot-aware

2014-02-04 Thread Josef Bacik
On 02/04/2014 03:52 PM, Kai Krakow wrote: Hi! I'm curious... The whole snapshot thing on btrfs is based on its COW design. But you can make individual files and directory contents nocow by applying the C attribute on it using chattr. This is usually recommended for database files and VM images.

Re: Are nocow files snapshot-aware

2014-02-04 Thread David Sterba
On Tue, Feb 04, 2014 at 08:22:05PM -0500, Josef Bacik wrote: On 02/04/2014 03:52 PM, Kai Krakow wrote: Hi! I'm curious... The whole snapshot thing on btrfs is based on its COW design. But you can make individual files and directory contents nocow by applying the C attribute on it using