If platform supports xfs filesystem then use xfs as default filesystem
for container rootfs instead of ext4. Reason being that ext4 is pre-allcating
lot of metadata (around 1.8GB on 100G thin volume) and that can take long
enough on AWS storage that systemd times out and docker fails to start.
If one disables pre-allocation of ext4 metadata, then it will be allocated
when containers are mounted and we will have multiple copies of metadata
per container. For a 100G thin device, it was around 1.5GB of metadata
per container.
ext4 has an optimization to skip zeroing if discards are issued and
underlying device guarantees that zero will be returned when discarded
blocks are read back. devicemapper thin devices don't offer that guarantee
so ext4 optimization does not kick in. In fact given discards are optional
and can be dropped on the floor if need be, it looks like it might not be
possible to guarantee that all the blocks got discarded and if read back
zero will be returned.
Signed-off-by: Anusha Ragunathan <anusha@docker.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
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