On 2018-07-18 13:40, Chris Murphy wrote:
On Wed, Jul 18, 2018 at 11:14 AM, Chris Murphy <li...@colorremedies.com> wrote:
I don't know for sure, but based on the addresses reported before and
after dd for the fallocated tmp file, it looks like Btrfs is not using
the originally fallocated addresses for dd. So maybe it is COWing into
new blocks, but is just as quickly deallocating the fallocated blocks
as it goes, and hence doesn't end up in enospc?
Previous thread is "Problem with file system" from August 2017. And
there's these reproduce steps from Austin which have fallocate coming
after the dd.
truncate --size=4G ./test-fs
mkfs.btrfs ./test-fs
mkdir ./test
mount -t auto ./test-fs ./test
dd if=/dev/zero of=./test/test bs=65536 count=32768
fallocate -l 2147483650 ./test/test && echo "Success!"
My test Btrfs is 2G not 4G, so I'm cutting the values of dd and
fallocate in half.
[chris@f28s btrfs]$ sudo dd if=/dev/zero of=tmp bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB, 1000 MiB) copied, 7.13391 s, 147 MB/s
[chris@f28s btrfs]$ sync
[chris@f28s btrfs]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg-btrfstest 2.0G 1018M 1.1G 50% /mnt/btrfs
[chris@f28s btrfs]$ sudo fallocate -l 1000m tmp
Succeeds. If I do it with a 1200M file for dd and fallocate 1200M over
it, this fails, but I kinda expect that because there's only 1.1G free
space. But maybe that's what you're saying is the bug, it shouldn't
fail?
Yes, you're right, I had things backwards (well, kind of, this does work
on ext4 and regular XFS, so it arguably should work here).
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