On Sat, Jan 24, 2015 at 01:06:01PM -0500, Zygo Blaxell wrote: > I am seeing a lot of spurious I/O errors that look like they come from > the cache-facing side of btrfs. While running a heavy load with some > extent-sharing (e.g. building 20 Linux kernels at once from source trees > copied with 'cp -a --reflink=always'), some files will return spurious > EIO on read. It happens often enough to prevent a Linux kernel build > about 1/3 of the time. [...] > Observed from 3.17..3.18.3. All filesystems affected use skinny-metadata. > No filesystems that are not using skinny-metadata seem to have this > problem.
I ran a test overnight using 3.18.3 on a freshly formatted filesystem with
no skinny-metadata.
The test consisted of creating reflink copies of a Linux kernel source
tree and running kernel builds in each copy simultaneously, like this:
# assume you have a ready-to-build kernel tree in 'linux'
for x in $(seq 1 5); do
cp -a --reflink linux linux-$x
done
# build all the kernels at once
for x in $(seq 1 5); do
(cd linux-$x && make -j10 2>&1 | tee make.log) &
done
wait
# then tail all the make.logs and see how many failed due to
# I/O errors
Spurious I/O errors occured with as few as two concurrent kernel builds.
The test machine has 16GB of RAM and the filesystem is also 16GB,
RAID1 on two spinning disks.
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