Roman Mamedov wrote on 2015/11/10 14:08 +0500:
On Tue, 10 Nov 2015 16:16:26 +0800
Qu Wenruo <quwenruo.bt...@gmx.com> wrote:
So if things are correct, the btrfs you converted should still be in
mixed-bg mode.
A recent 'btrfs fi df' command should show things like:
Data+Metadata, DUP: total=512.00MiB, used=68.23MiB
Actually not quite. After all the rebalancing, I currently have:
Data, single: total=8.37TiB, used=7.50TiB
System, DUP: total=32.00MiB, used=592.00KiB
Metadata, DUP: total=8.00GiB, used=6.42GiB
GlobalReserve, single: total=512.00MiB, used=0.00B
But as we know recently there were reports that it now causes corruption or
does not work. So I wonder what happened that broke it, and is there really no
simpler fix? Even if requiring the user to balance to get rid of the bloated
Metadata like I had to.
Yes, current btrfs-convert has problem on marking chunk meta or data.
Resulting some data extents may lay in metadata chunk, and vice verse.
At least it won't pass latest btrfsck.
In that incorrect chunk layout, I'm not surprised any thing go wrong.
Made an experiment:
# dd if=/dev/zero bs=1M count=1 seek=100000 of=100G
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0023896 s, 439 MB/s
# losetup /dev/loop7 100G
# mkfs.ext4 /dev/loop7
// Success
# mount /dev/loop7 /mnt/tmp1/
// Copy some files there
# df -h /mnt/tmp1/
Filesystem Size Used Avail Use% Mounted on
/dev/loop7 96G 2.6G 89G 3% /mnt/tmp1
# umount /mnt/tmp1/
# btrfs-convert -d /dev/loop7
creating btrfs metadata.
creating ext2fs image file.
cleaning up system chunk.
conversion complete.
Here call 'btrfsck' from *latest* btrfs-progs.
You'll see tons of error, showing problems including:
1) stripes cross map boundary
This will lead to kernel BUG_ON() when scrubbing.
2) Data extents in metadata chunks
The problem causing the metadata accounting goes crazy.
# mount /dev/loop7 /mnt/tmp1/
# btrfs fi df /mnt/tmp1/
Data, single: total=65.00GiB, used=1.32GiB
System, single: total=32.00MiB, used=12.00KiB
Metadata, single: total=32.63GiB, used=2.91GiB
GlobalReserve, single: total=92.00MiB, used=0.00B
And your btrfs-convert is already broken, with wrong chunk allocation.
# btrfs sub del /mnt/tmp1/ext2_saved
Transaction commit: none (default)
Delete subvolume '/mnt/tmp1/ext2_saved'
# btrfs fi df /mnt/tmp1/
Data, single: total=10.00GiB, used=120.12MiB
System, single: total=32.00MiB, used=4.00KiB
Metadata, single: total=4.00GiB, used=2.37GiB
GlobalReserve, single: total=52.00MiB, used=0.00B
// It has 2.6 GB of files, and most of them are now accounted as "Metadata".
# btrfs fi balance start -m /mnt/tmp1/
Done, had to relocate 5 out of 7 chunks
// They are now reclassified as data:
# btrfs fi df /mnt/tmp1/
Data, single: total=10.00GiB, used=2.49GiB
System, single: total=32.00MiB, used=4.00KiB
Metadata, single: total=1.00GiB, used=468.00KiB
GlobalReserve, single: total=4.00MiB, used=0.00B
// Unmount, mount, checked all files integrity with 'cfv', all files are
present and there is no corruption.
So this behaves just like I remember it to, after conversion at first a large
part of the data will show up as Metadata, but a balance fixes that. And most
importantly no corruption issues. Maybe it's just because this is only a small
test FS, but my production one earlier went through the same process without
problems as well.
Yes, some problem can be fixed by such balance, as after balance, data
and metadata will be relocated to correct new chunks.
But there may be a lot of hidden bugs here.
And we can't ignore such malfunction just because it's OK under some
cases, or btrfs won't really become a production ready filesystem.
Thanks,
Qu
Using btrfs-tools v3.17 and kernel 3.18.21
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
