Q: list btrfs snapshots/subvolumes

Q: list btrfs snapshots/subvolumes

[Adrian von Bidder]

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Heyho!

I'm currently (once more) trying to experiment with btrfs, especially since 
the ENOSPC handling and "delete snapshots/subvolumes" make it look extremely 
appealing now.

Some questions:
 * how do I list available snapshots/subvolumes?
 * assuming a disk has failed: just to be sure:
   "btrfs-vol -r missing" will remove the missing device.  Not sure: will it 
also replicate the missing copies of my (raid1) data and metadata?  Given that 
it takes ages (ok, just running a few minutes now ;-) to run on this system, 
I'd assume so.  Or is a separate "btrfs-vol -b" necessary?
 * "subvolume" and "snapshot" is technically the same, except that a subvolume 
is created empty and a snapshot is a cow copy of an existing tree.  Handling 
these two is the same once they're created?

Ok, that's what I can think of right now.  Eagerly waiting for "set default 
subvolume to be mounted" to be written... :-)

I just did a few tests with a 4 x 450G raid 1 btrfs volume: adding some 5G of 
small files, remove a disk (didn't pull it out, but shut down the system 
first), remove failing disk, re-add a disk.  So far it seems to work just 
fine.  Just a curiosity: it seems to distribute all data between only two of 
the disks, the other two stay empty.  Is that desired behaviour?  Wouldn't it 
be more efficient to distribute data across all disks?

(everything with 2.6.32-rc8. Filesystem was created with btrfs-tools 0.19.)

cheers
-- vbi

(((
P.S.: since recovery after disk failure is a tense moment where I don't want 
to have to hunt around for the answer ...:

--- a/btrfs-vol.c
+++ b/btrfs-vol.c
@@ -53,6 +53,8 @@ static void print_usage(void)
        fprintf(stderr, "\t-a device add one device\n");
        fprintf(stderr, "\t-b balance chunks across all devices\n");
        fprintf(stderr, "\t-r device remove one device\n");
+       fprintf(stderr, "\t   use 'missing' as device name "
+               "to remove a failed device\n");
        exit(1);
 }
)))


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Re: Q: list btrfs snapshots/subvolumes

[TARUISI Hiroaki]

> 
> Some questions:
>  * how do I list available snapshots/subvolumes?

As for this question, we will soon be able to list available
snapshots/subvolumes with btrfsctl utility.
But for now, we should count number of BTRFS_ROOT_ITEMs with
btrfs-debug-tree or so.

Regards,
taruisi