incremental send/receive ERROR: cannot find parent subvolume

incremental send/receive ERROR: cannot find parent subvolume

[Emil.s]

Hello,

I'm trying to restore a subvolume from a backup, but I'm failing when
I try to setup the replication chain again.

Previously I had disk A and B, where I was sending snapshots from A to
B using "send -c /disk_a/1 /disk_a/2 | receive /disk_b" and so on.
Now disk A failed, so I got a new disk: C.

First I sent the last backup from B to C by running "send disk_b/2 |
receive /disk_c/".

Then my plan was to use disk B as the new main disk, so on disk B, I
created a new snapshot by running "snapshot -r disk_b/2
disk_b/my_volume".
Now I want to send "disk_b/my_volume" to disk C, so that I can set
disk_b/2 to RW and start using it again, but the last send fails with
"ERROR: cannot find parent subvolume".

Disk B:
root@tillberga: /backup #> btrfs subvol sh snapshots/user_data_2018-02-17/
snapshots/user_data_2018-02-17
Name: user_data_2018-02-17
UUID: 93433261-d954-9f4b-8319-d450ae079a9a
Parent UUID: 51180286-c202-c94c-b8f9-2ecc8d2b5b7c
Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
Flags: readonly
Snapshot(s):
user_data_test

Disk C:
root@hedemora: /btrfs #> btrfs subvol sh user_data_2018-02-17/
user_data_2018-02-17
Name: user_data_2018-02-17
UUID: 35361429-a42c-594b-b390-51ffb9725324
Parent UUID: -
Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a
Flags: readonly
Snapshot(s):

Disk B has UUID 93433261-d954-9f4b-8319-d450ae079a9a, and disk C has
"Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a". I think that's
alright?

The new snapshot on disk B looks as following:
root@tillberga: /backup #> btrfs subvol sh user_data_test
user_data_test
Name: user_data_test
UUID: bf88000c-e3a6-434b-8f69-f5ce2174227e
Parent UUID: 93433261-d954-9f4b-8319-d450ae079a9a
Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
Flags: readonly
Snapshot(s):

But when I'm trying to send it, I'm getting the following:
root@tillberga: /backup #> btrfs send -v -c
snapshots/user_data_2018-02-17 user_data_test | ssh user@hedemora
"sudo btrfs receive -v /btrfs/"
At subvol user_data_test
BTRFS_IOC_SEND returned 0
joining genl thread
receiving snapshot user_data_test
uuid=014fc004-ae04-0148-9525-1bf556fd4d10, ctransid=52373
parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10,
parent_ctransid=52373
At snapshot user_data_test
ERROR: cannot find parent subvolume

Note that the receiver says
"parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10". Not really sure
where that comes from, but disk B has the same, so maybe that's the
UUID of the original snapshot on disk A?

Is it possible to continue to send incremental snapshots between these
two file systems, or must I do a full sync?

Re: incremental send/receive ERROR: cannot find parent subvolume

[Hans van Kranenburg]

On 02/26/2018 11:54 PM, Emil.s wrote:
> Hello,
> 
> I'm trying to restore a subvolume from a backup, but I'm failing when
> I try to setup the replication chain again.
> 
> Previously I had disk A and B, where I was sending snapshots from A to
> B using "send -c /disk_a/1 /disk_a/2 | receive /disk_b" and so on.
> Now disk A failed, so I got a new disk: C.
> 
> First I sent the last backup from B to C by running "send disk_b/2 |
> receive /disk_c/".

I can't read all of it right now, my time is a bit limited, but I have a
quick suggestion to at least make the original goal work, I think.

The list of snapshots that were on your A was organized differently than
the list with the same numbers 1, 2, 3 on B.

On A, you always snapshot the main r/w subvolume.

A
\_ A1
\_ A2
\_ A3

On B, every time you receive based on a previous one, it snapshots the
previous one and then puts changes on top:

B1 (received from A1)
\_ B2 (snap from B1, with changes from A1->A2)
   \_ B3 (snap from B2, with changes from A2->A3)
      \_ etc...

If A is gone, and you have new empty C:

> Then my plan was to use disk B as the new main disk, so on disk B, I
> created a new snapshot by running "snapshot -r disk_b/2
> disk_b/my_volume".
> Now I want to send "disk_b/my_volume" to disk C, so that I can set
> disk_b/2 to RW and start using it again, but the last send fails with
> "ERROR: cannot find parent subvolume".

Do it like this:

-# btrfs snap B2 my_volume (so no -r)

now my_volume is a writable clone of B2

-# btrfs snap -r my_volume my_volume1

now you start a new line of snapshots where my_volume has the same role
as A before.

my_volume
\_ my_volume1
\_ my_volume2
\_ my_volume3

Now you can send my_volume3 -p my_volume2 etc...

Then you discard all old Bx whenever you want.

In the following, disk_b/2 and your other example names are suddenly
replaced by real names, which makes it a bit hard to follow quickly.

> Disk B:
> root@tillberga: /backup #> btrfs subvol sh snapshots/user_data_2018-02-17/
> snapshots/user_data_2018-02-17
> Name: user_data_2018-02-17
> UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Parent UUID: 51180286-c202-c94c-b8f9-2ecc8d2b5b7c
> Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
> Flags: readonly
> Snapshot(s):
> user_data_test
> 
> Disk C:
> root@hedemora: /btrfs #> btrfs subvol sh user_data_2018-02-17/
> user_data_2018-02-17
> Name: user_data_2018-02-17
> UUID: 35361429-a42c-594b-b390-51ffb9725324
> Parent UUID: -
> Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Flags: readonly
> Snapshot(s):
> 
> Disk B has UUID 93433261-d954-9f4b-8319-d450ae079a9a, and disk C has
> "Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a". I think that's
> alright?
> 
> The new snapshot on disk B looks as following:
> root@tillberga: /backup #> btrfs subvol sh user_data_test
> user_data_test
> Name: user_data_test
> UUID: bf88000c-e3a6-434b-8f69-f5ce2174227e
> Parent UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
> Flags: readonly
> Snapshot(s):
> 
> But when I'm trying to send it, I'm getting the following:
> root@tillberga: /backup #> btrfs send -v -c
> snapshots/user_data_2018-02-17 user_data_test | ssh user@hedemora
> "sudo btrfs receive -v /btrfs/"
> At subvol user_data_test
> BTRFS_IOC_SEND returned 0
> joining genl thread
> receiving snapshot user_data_test
> uuid=014fc004-ae04-0148-9525-1bf556fd4d10, ctransid=52373
> parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10,
> parent_ctransid=52373
> At snapshot user_data_test
> ERROR: cannot find parent subvolume
> 
> Note that the receiver says
> "parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10". Not really sure
> where that comes from, but disk B has the same, so maybe that's the
> UUID of the original snapshot on disk A?
> 
> Is it possible to continue to send incremental snapshots between these
> two file systems, or must I do a full sync?


-- 
Hans van Kranenburg

Re: incremental send/receive ERROR: cannot find parent subvolume

[Andrei Borzenkov]

27.02.2018 01:54, Emil.s пишет:
> Hello,
> 
> I'm trying to restore a subvolume from a backup, but I'm failing when
> I try to setup the replication chain again.
> 
> Previously I had disk A and B, where I was sending snapshots from A to
> B using "send -c /disk_a/1 /disk_a/2 | receive /disk_b" and so on.
> Now disk A failed, so I got a new disk: C.
> 
> First I sent the last backup from B to C by running "send disk_b/2 |
> receive /disk_c/".
> 
> Then my plan was to use disk B as the new main disk, so on disk B, I
> created a new snapshot by running "snapshot -r disk_b/2
> disk_b/my_volume".
> Now I want to send "disk_b/my_volume" to disk C, so that I can set
> disk_b/2 to RW and start using it again, but the last send fails with
> "ERROR: cannot find parent subvolume".
> 
> Disk B:
> root@tillberga: /backup #> btrfs subvol sh snapshots/user_data_2018-02-17/
> snapshots/user_data_2018-02-17
> Name: user_data_2018-02-17
> UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Parent UUID: 51180286-c202-c94c-b8f9-2ecc8d2b5b7c
> Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
> Flags: readonly
> Snapshot(s):
> user_data_test
> 
> Disk C:
> root@hedemora: /btrfs #> btrfs subvol sh user_data_2018-02-17/
> user_data_2018-02-17
> Name: user_data_2018-02-17
> UUID: 35361429-a42c-594b-b390-51ffb9725324
> Parent UUID: -
> Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Flags: readonly
> Snapshot(s):
> 
> Disk B has UUID 93433261-d954-9f4b-8319-d450ae079a9a, and disk C has
> "Received UUID: 93433261-d954-9f4b-8319-d450ae079a9a". I think that's
> alright?
> 
> The new snapshot on disk B looks as following:
> root@tillberga: /backup #> btrfs subvol sh user_data_test
> user_data_test
> Name: user_data_test
> UUID: bf88000c-e3a6-434b-8f69-f5ce2174227e
> Parent UUID: 93433261-d954-9f4b-8319-d450ae079a9a
> Received UUID: 014fc004-ae04-0148-9525-1bf556fd4d10
> Flags: readonly
> Snapshot(s):
> 
> But when I'm trying to send it, I'm getting the following:
> root@tillberga: /backup #> btrfs send -v -c
> snapshots/user_data_2018-02-17 user_data_test | ssh user@hedemora
> "sudo btrfs receive -v /btrfs/"
> At subvol user_data_test
> BTRFS_IOC_SEND returned 0
> joining genl thread
> receiving snapshot user_data_test
> uuid=014fc004-ae04-0148-9525-1bf556fd4d10, ctransid=52373
> parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10,
> parent_ctransid=52373
> At snapshot user_data_test
> ERROR: cannot find parent subvolume
> 
> Note that the receiver says
> "parent_uuid=014fc004-ae04-0148-9525-1bf556fd4d10". Not really sure
> where that comes from, but disk B has the same, so maybe that's the
> UUID of the original snapshot on disk A?
> 


If "Received UUID" is set on a subvolume, "btrfs send" will forward it
and set on destination unchanged, instead of computing "correct"
Received UUID. This has been discussed several times.

> Is it possible to continue to send incremental snapshots between these
> two file systems, or must I do a full sync?

You would need to create writable clone on B first and start with this
clone; new writable clone won't have (misleading) Received UUID and you
start clean.