This is with my small 256 MiB btrfs mixed-bg dup-mode /boot, or actually,
with its backup (same size partition, different device). Kernel 3.17.0,
btrfs-progs 3.16.1 (both actually from git), gentoo.
It was time to renew my backups so I did a mkfs.btrfs on the backup to
start fresh:
mkfs.btrfs -d dup -m dup -L bt0238gcn0+35l0 -O extref,skinny-metadata,no-
holes -f /dev/sdb3
Of course with the 256 MiB size, mkfs.btrfs naturally added mixed-bg to
the features as well.
I then did a balance to remove the single-mode mkfs-time artifacts.
Mount-options on both the working and backup filesystems are identical:
nodev,nosuid,noauto,compress=lzo,autodefrag
Mounting both filesystems, I then tried to use mc to copy everything from
the working filesystem to the mkfs-fresh backup. That failed with
enospc. However, in the past, repeated copy attempts, using "if size
differs" when mc pops up the duplicate filename warnings, have eventually
copied everything over just fine.
This time, while repeated copy attempts did result in most files copying,
the (dracut generated) cpio archive that gets appended to my kernels as
the initramfs failed to copy over.
However, the source filesystem is an identically sized btrfs with the
same mount options (and I think the same features enabled, tho I'm not
sure), and the files fit there with "plenty" (for the fs size) of room to
spare!
And both btrfs filesystem show and btrfs filesystem df say there's lots
of room left.
Destination filesystem (without the 14905 KiB cpio file, #>> indicates
the prompt):
#>>btrfs filesystem show /bk/bt
Label: 'bt0238gcn0+35l0' uuid: 4d310294-c899-4dcc-be81-580d477060e9
Total devices 1 FS bytes used 30.59MiB
devid 1 size 256.00MiB used 132.00MiB path /dev/sdb3
Btrfs v3.16.1
#>>btrfs filesystem df /bk/bt
System, DUP: total=16.00MiB, used=4.00KiB
Data+Metadata, DUP: total=50.00MiB, used=30.59MiB
GlobalReserve, single: total=4.00MiB, used=0.00
Source filesystem (including the 14905 KiB cpio file):
c#>>btrfs filesystem show /bt
Label: 'bt0238gcn1+35l0' uuid: d6539322-0834-4eeb-928d-a13eb32dcbb2
Total devices 1 FS bytes used 44.48MiB
devid 1 size 256.00MiB used 159.00MiB path /dev/sda3
Btrfs v3.16.1
#>>btrfs filesystem df /bt
System, DUP: total=15.50MiB, used=4.00KiB
Data+Metadata, DUP: total=64.00MiB, used=44.48MiB
GlobalReserve, single: total=4.00MiB, used=0.00
On the destination, 50 MiB data+metadata allocated - 30.59 MiB used =
19.41 MiB free in the chunk(s). So an approximately 14.6 MiB file
shouldn't even require additional chunk allocation. But as can be seen
from the show output, even if it did, there's plenty of unallocated space
left to allocate new chunks if need be.
So why am I getting enospc?
FWIW, if I try to cp it instead of using mc, 14208 KiB copies before I
get the enospc.
At that point, with the partially copied (14208/14905 KiB) file, this is
what I get:
#>>btrfs filesystem show /bk/bt
Label: 'bt0238gcn0+35l0' uuid: 4d310294-c899-4dcc-be81-580d477060e9
Total devices 1 FS bytes used 43.59MiB
devid 1 size 256.00MiB used 132.00MiB path /dev/sdb3
Btrfs v3.16.1
#>>btrfs filesystem df /bk/bt
System, DUP: total=16.00MiB, used=4.00KiB
Data+Metadata, DUP: total=50.00MiB, used=43.58MiB
GlobalReserve, single: total=4.00MiB, used=0.00
So no further chunk allocation, data+metadata usage increased from 30.59
MiB to 43.58 MiB, almost exactly 13 MiB. The file is 14905 MiB and 14208
copied but it couldn't handle that last ~700 KiB, even tho data+metadata
still shows nearly 6.5 MiB still unused in the existing chunk and there's
still 124 MiB unallocated, nearly half the 256 MiB filesystem size! That
can be halved due to dup-mode for ~62 MiB of usable space, barring bugs
like this one.
And it all fits on the basically identical source btrfs, with 97 MiB
still unallocated to chunks and 19+ MiB free in the data+metadata
chunks. So why is the new filesystem prematurely enospcing me?
I can btrfs image the filesystems if necessary, and/or even dd-image them
and send the whole thing, tho it /does/ have kernel config and system-
maps, etc as well as my grub2 config, so while it's not too private it's
probably not something I want on a public list. Tho I'd guess it to be a
reasonably generic issue to duplicate, given the information above.
--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman
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