[lxc-users] writeback cache for all container processes?

[Fajar A. Nugraha]

On Mon, Feb 2, 2015 at 8:35 PM, Fajar A. Nugraha <list at fajar.net> wrote:

> On Mon, Feb 2, 2015 at 7:45 PM, Tomasz Chmielewski <mangoo at wpkg.org>
> wrote:
>
>>
>>> If you want to disable sync for the container, the best you can do is
>>> probably use some filesystem that can do so. For example, zfs has
>>> "sync=disabled" per-dataset settings. So you can have "sync=standard"
>>> for filesystems used by the host, and "sync=disabled" for filesystems
>>> used by containers.
>>>
>>
>> That's a weird advice, given that lxc are Linux containers, and ZFS is
>> not in Linux kernel (I know that there are some 3rd party porting attempts,
>> but it's not really applicable in many situations).
>>
>>
> Honestly, that's the best advice I can give. It's straightforward, simple,
> and works.
>
> There are lots of zfsonlinux users using it on production environment.
> Even lxc-create supports zfs as backingstore, to a degree (man lxc-create).
> And doing the above is the equivalent of having eatmydata running on
> everything that access that dataset.
>
>

FYI, this is what I just tested on ubuntu utopic with lxc 1.1.0 from daily
ppa

# zfs get sync,compression rpool/lxc
NAME       PROPERTY     VALUE     SOURCE
rpool/lxc  sync         disabled  inherited from rpool
rpool/lxc  compression  lz4       inherited from rpool

# lxc-create -B zfs --zfsroot=rpool/lxc -t download -n test -- -d ubuntu -r
utopic -a amd64
Using image from local cache
Unpacking the rootfs

---
You just created an Ubuntu container (release=utopic, arch=amd64,
variant=default)

To enable sshd, run: apt-get install openssh-server

For security reason, container images ship without user accounts
and without a root password.

Use lxc-attach or chroot directly into the rootfs to set a root password
or create user accounts.

# df -h | grep test
rpool/lxc/test            46G  184M   46G   1% /var/lib/lxc/test/rootfs

# zfs get sync,compression,compressratio,used,logicalused rpool/lxc/test
NAME            PROPERTY       VALUE     SOURCE
rpool/lxc/test  sync           disabled  inherited from rpool
rpool/lxc/test  compression    lz4       inherited from rpool
rpool/lxc/test  compressratio  2.04x     -
rpool/lxc/test  used           183M      -
rpool/lxc/test  logicalused    371M      -

# lxc-start -n test

# lxc-ls -f --running
NAME  STATE    IPV4        IPV6  GROUPS  AUTOSTART
--------------------------------------------------
test  RUNNING  10.0.4.111  -     -       NO

# lxc-attach -n test -- hostname
test

# lxc-attach -n test -- df -h
Filesystem      Size  Used Avail Use% Mounted on
rpool/lxc/test   46G  142M   46G   1% /
cgroup           12K     0   12K   0% /sys/fs/cgroup
none            100K  4.0K   96K   4% /dev
none            4.0K     0  4.0K   0% /sys/fs/cgroup/cgmanager
none            1.2G   48K  1.2G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            5.9G     0  5.9G   0% /run/shm
none            100M     0  100M   0% /run/user

# lxc-stop -n test

-- 
Fajar
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