Re: Receive on same subvolume

[Matthew Lai <m@matthewlai.ca>]

On 03/02/2014 11:26 AM, Chris Murphy wrote:
> On Feb 3, 2014, at 11:19 AM, Matthew Lai <m@matthewlai.ca> wrote:
>
>> Thanks. I should clarify what I'm trying to do.
>>
>> I'm trying to use btrfs send for backup, without having another btrfs volume.
>>
>> So the initial backup is a complete send, piped to Amazon Glacier (so my machine never has the whole file, and doesn't have space for one).
> OK so you've use btrfs send piped to Glacier which creates a *file*, I'll call it "initial", not a navigable directory of files? Right?
That is correct.
>> It looks like the problem now is the sent file can't be applied to the original volume (for restore).
> I'm counting two sent files: initial, increment1. I'm not sure which one you're applying. If you have the exact same read-only snapshot that the btrfs send file "initial" is based on, then you'd apply the increment1 to that read-only snapshot which will cause a new read-only snapshot to be created with the incremental data applied to it. The error you're getting sounds like the parent read-only snapshot isn't available?
>
That is also correct. There are 2 sent files. I am trying to apply 
increment1, on a snapshot of the parent (that was used to create 
increment1).

I added -vv. Here is the test script for reproducing this entire setup.

-----------------------------------------------------------------------
#!/bin/sh

btrfs subvolume create data
btrfs subvolume snapshot -r data first_backup
touch data/a
btrfs subvolume snapshot -r data second_backup
btrfs send -p first_backup second_backup > increment
btrfs subvolume snapshot first_backup first_backup_rw
btrfs receive -vv first_backup_rw < increment
-----------------------------------------------------------------------

Output:
-----------------------------------------------------------------------
Create subvolume './data'
Create a readonly snapshot of 'data' in './first_backup'
Create a readonly snapshot of 'data' in './second_backup'
At subvol second_backup
Create a snapshot of 'first_backup' in './first_backup_rw'
At snapshot second_backup
receiving snapshot second_backup 
uuid=e6159a2a-3430-344a-a23d-b9bb83851a63, ctransid=28 
parent_uuid=20c4ff66-a9ec-fc44-93c6-2c12637e95e6, parent_ctransid=26
ERROR: could not find parent subvolume
-----------------------------------------------------------------------

I would think applying the "patch" to first_backup_rw should succeed, 
because it's exactly the same as first_backup, which is the parent for 
the send, but it doesn't.

Thanks
Matthew