Public bug reported:
I've been running some scale tests for LXD and what I've noticed is that
"zfs clone" gets slower and slower as the zfs filesystem is getting
busier.
It feels like "zfs clone" requires some kind of pool-wide lock or
something and so needs for all operations to complete before it can
clone a new filesystem.
A basic LXD scale test with btrfs vs zfs shows what I mean, see below
for the reports.
The test is run on a completely dedicated physical server with the pool
on a dedicated SSD, the exact same machine and SSD was used for the
btrfs test.
The zfs filesystem is configured with those settings:
- relatime=on
- sync=disabled
- xattr=sa
So it shouldn't be related to pending sync() calls...
The workload in this case is ultimately 1024 containers running busybox as
their init system and udhcpc grabbing an IP.
The problem gets significantly worse if spawning busier containers, say a full
Ubuntu system.
=== zfs ===
root@edfu:~# /home/ubuntu/lxd-benchmark spawn --count=1024
--image=images:alpine/edge/amd64 --privileged=true
Test environment:
Server backend: lxd
Server version: 2.0.0.rc8
Kernel: Linux
Kernel architecture: x86_64
Kernel version: 4.4.0-16-generic
Storage backend: zfs
Storage version: 5
Container backend: lxc
Container version: 2.0.0.rc15
Test variables:
Container count: 1024
Container mode: privileged
Image: images:alpine/edge/amd64
Batches: 128
Batch size: 8
Remainder: 0
[Apr 3 06:42:51.170] Importing image into local store:
64192037277800298d8c19473c055868e0288b039349b1c6579971fe99fdbac7
[Apr 3 06:42:52.657] Starting the test
[Apr 3 06:42:53.994] Started 8 containers in 1.336s
[Apr 3 06:42:55.521] Started 16 containers in 2.864s
[Apr 3 06:42:58.632] Started 32 containers in 5.975s
[Apr 3 06:43:05.399] Started 64 containers in 12.742s
[Apr 3 06:43:20.343] Started 128 containers in 27.686s
[Apr 3 06:43:57.269] Started 256 containers in 64.612s
[Apr 3 06:46:09.112] Started 512 containers in 196.455s
[Apr 3 06:58:19.309] Started 1024 containers in 926.652s
[Apr 3 06:58:19.309] Test completed in 926.652s
=== btrfs ===
Test environment:
Server backend: lxd
Server version: 2.0.0.rc8
Kernel: Linux
Kernel architecture: x86_64
Kernel version: 4.4.0-16-generic
Storage backend: btrfs
Storage version: 4.4
Container backend: lxc
Container version: 2.0.0.rc15
Test variables:
Container count: 1024
Container mode: privileged
Image: images:alpine/edge/amd64
Batches: 128
Batch size: 8
Remainder: 0
[Apr 3 07:42:12.053] Importing image into local store:
64192037277800298d8c19473c055868e0288b039349b1c6579971fe99fdbac7
[Apr 3 07:42:13.351] Starting the test
[Apr 3 07:42:14.793] Started 8 containers in 1.442s
[Apr 3 07:42:16.495] Started 16 containers in 3.144s
[Apr 3 07:42:19.881] Started 32 containers in 6.530s
[Apr 3 07:42:26.798] Started 64 containers in 13.447s
[Apr 3 07:42:42.048] Started 128 containers in 28.697s
[Apr 3 07:43:13.210] Started 256 containers in 59.859s
[Apr 3 07:44:26.238] Started 512 containers in 132.887s
[Apr 3 07:47:30.708] Started 1024 containers in 317.357s
[Apr 3 07:47:30.708] Test completed in 317.357s
** Affects: zfs-linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1567557
Title:
Performance degradation of "zfs clone" when under load
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