On 2016-11-16 06:04, Martin Steigerwald wrote:
Am Mittwoch, 16. November 2016, 16:00:31 CET schrieb Roman Mamedov:
On Wed, 16 Nov 2016 11:55:32 +0100
Martin Steigerwald <martin.steigerw...@teamix.de> wrote:
I do think that above kernel messages invite such a kind of interpretation
tough. I took the "BTRFS: open_ctree failed" message as indicative to some
structural issue with the filesystem.
For the reason as to why the writable mount didn't work, check "btrfs fi df"
for the filesystem to see if you have any "single" profile chunks on it:
quite likely you did already mount it "degraded,rw" in the past *once*,
after which those "single" chunks get created, and consequently it won't
mount r/w anymore (without lifting the restriction on the number of missing
devices as proposed).
That exactly explains it. I very likely did a degraded mount without ro on
this disk already.
Funnily enough this creates another complication:
merkaba:/mnt/zeit#1> btrfs send somesubvolume | btrfs receive /mnt/
someotherbtrfs
ERROR: subvolume /mnt/zeit/somesubvolume is not read-only
Yet:
merkaba:/mnt/zeit> btrfs property get somesubvolume
ro=false
merkaba:/mnt/zeit> btrfs property set somesubvolume ro true
ERROR: failed to set flags for somesubvolume: Read-only file system
To me it seems right logic would be to allow the send to proceed in case
the whole filesystem is readonly.
It should, but doesn't currently. There was a thread about this a while
back, but I don't think it ever resulted in anything changing.
As there seems to be no force option to override the limitation and I
do not feel like compiling my own btrfs-tools right now, I will use rsync
instead.
In a case like this, I'd trust rsync more than send/receive. The
following rsync switches might also be of interest:
-a: This turns on a bunch of things almost everyone wants when using
rsync, similar to the same switch for cp, just with even more added in.
-H: This recreates hardlinks on the receiving end.
-S: This recreates sparse files.
-A: This copies POSIX ACL's
-X: This copies extended attributes (most of them at least, there are a
few that can't be arbitrarily written to).
Pre-creating the subvolumes by hand combined with using all of those
will get you almost everything covered by send/receive except for
sharing of extents and ctime.
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