viernes, 12 de junio de 2015

...Docker and devicemapper`s thinpool in RHEL 7

I’ve been working with Docker this week, for an OpenShift v3 demo, and I’ve been struggling with storage for docker, so here are my notes, just in case anyonw needs the, or I do need them again.
Docker in RHEL7 is recommended to use devicemapper storage drive with thin provisioning. I was setting up some Vagrant boxes for my environment, and I was running into issues with pulling down of images never finishing, or errors while writing into the docker storage. It seems that my VM was created with a very small ammount of disc space for docker, so it could not properly run. This is how I diagnosed the problem and how I fixed it.
Kudos to Nick Strugnell for helping me out.

Diagnose

Once I did a docker pull, and got stuck, I needed to know what was the problem, so first thing, inspect LVM to see configuration.
LVM is Logical VOlume Manager and has 3 concepts:
  • PV (Physical Volume): This is the classic HDD
  • VG (Volume Group): This can span multiple Physical Volumes
  • LV (Logical Volume): This would be the volumes, directly usable by the apps.
For every type, there is a set of commands, easy to understand that help us:
  • pvs (Physical Volume Summary), pvcreate (create a Physical Volume), pvchange, pvck, pvdisplay, pvmove, pvremove, pvresize, pvscan
  • vgs (Volume Group summary), vgcfgbackup, vgchange, vgconvert, vgdisplay, vgextend, vgimportclone, vgmknodes, vgremove, vgsplit, vgcfgrestore, vgck, vgcreate, vgexport, vgimport, vgmerge, vgreduce, vgrename, vgscan
  • lvs (Logical Volume Summary), lvchange, lvcreate, lvextend, lvremove, lvresize, lvscan, lvconvert, lvdisplay, lvreduce, lvrename
I did a summary of my VM:
[root@ose3-helper ~]# pvs
  PV         VG         Fmt  Attr PSize PFree
  /dev/vda3  VolGroup00 lvm2 a--  9.78g    0

[root@ose3-helper ~]# vgs
  VG         #PV #LV #SN Attr   VSize VFree
  VolGroup00   1   3   0 wz--n- 9.78g    0

[root@ose3-helper ~]# lvs
  LV          VG         Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  LogVol00    VolGroup00 -wi-ao----   7.97g
  LogVol01    VolGroup00 -wi-ao----   1.50g
  docker-pool VolGroup00 twi-aot-M- 256.00m             100.00 0.22
It looks like my docker-pool is full, and very small. So here is the problem.

Why is it using a docker-pool LV?

In RHEL 7 docker is configured to run with devicemapper, as seen here:
[root@ose3-helper ~]# cat /etc/sysconfig/docker-storage
DOCKER_STORAGE_OPTIONS=-s devicemapper --storage-opt dm.fs=xfs --storage-opt dm.thinpooldev=/dev/mapper/VolGroup00-docker--pool

How can I configure devicemapper for docker?

In order to use dm.thinpooldev you must have an LVM thinpool available, the docker-storage-setup package will assist you in configuring LVM. However you must provision your host to fit one of these three scenarios :
  • Root filesystem on LVM with free space remaining on the volume group. Run docker-storage-setup with no additional configuration, it will allocate the remaining space for the thinpool.
  • A dedicated LVM volume group where you’d like to reate your thinpool
echo <<EOF > /etc/sysconfig/docker-storage-setup
VG=docker-vg
SETUP_LVM_THIN_POOL=yes
EOF
docker-storage-setup
  • A dedicated block device, which will be used to create a volume group and thinpool
cat <<EOF > /etc/sysconfig/docker-storage-setup
DEVS=/dev/vdc
VG=docker-vg
SETUP_LVM_THIN_POOL=yes
EOF
docker-storage-setup
Once complete you should have a thinpool named docker-pool and docker should be configured to use it in /etc/sysconfig/docker-storage.
# lvs
LV                  VG        Attr       LSize  Pool Origin Data%  Meta% Move Log Cpy%Sync Convert
docker-pool         docker-vg twi-a-tz-- 48.95g             0.00   0.44

# cat /etc/sysconfig/docker-storage
DOCKER_STORAGE_OPTIONS=--storage-opt dm.fs=xfs --storage-opt dm.thinpooldev=/dev/mapper/openshift--vg-docker--pool

If you had previously used docker with loopback storage you should clean out /var/lib/docker This is a destructive operation and will delete all images and containers on the host.
systemctl stop docker
rm -rf /var/lib/docker/*
systemctl start docker

This topic is completelly taken from Erik Jacobs OSEv3 training. So kudos to him.

Solution

As I didn’t have enough free space in my VG and I couldn’t unmount LogVol00 to reduce the size what I did was:
  • Add a second drive to the KVM VM (With VirtManager, although virsh should work the same)
  • Add the PV
  • Resize the VG to consume the just added PV
  • Two options:
    • Resize the docker LV (easier)
    • Delete the docker LV and recreate it.
      • Stop docker
      • Delete /var/lib/docker/*
      • Delete the docker LV
      • rerun the docker-storage-setup to reconfigure the docker LV to have all the added space
      • Start docker

Add a second drive to the KVM VM

With Virt Manager, Just select the VM to where you want to add the drive, "open the terminal for the VM", press configuration (the light bulb), and click on "+ Add Hardware". Select the size, and VirtIO as the bus.

Add the PV

To see the name of the new disc, you can cat /proc/partitions:
[root@ose3-helper ~]# cat /proc/partitions
major minor  #blocks  name

 252        0   11534336 vda
 252        1       1024 vda1
 252        2     204800 vda2
 252        3   10278912 vda3
 253        0    1572864 dm-0
 253        1    8355840 dm-1
 253        2      32768 dm-2
 253        3     262144 dm-3
 253        4     262144 dm-4
 253        5   10485760 dm-5
 252       16    8388608 vdb
We can see that the disc I just added is vdb, so I will add a PV for it with pvcreate:
[root@ose3-helper ~]# pvcreate /dev/vdb
  Physical volume "/dev/vdb" successfully created
And list it with pvs:
[root@ose3-helper ~]# pvs
  PV         VG         Fmt  Attr PSize PFree
  /dev/vda3  VolGroup00 lvm2 a--  9.78g    0
  /dev/vdb              lvm2 ---  8.00g 8.00g

Resize the VG to consume the just added PV

Now I need to make the VG span to this PV, so I will vgextend (I will list before and after to see the changes):
[root@ose3-helper ~]# vgs
  VG         #PV #LV #SN Attr   VSize VFree
  VolGroup00   1   3   0 wz--n- 9.78g    0

[root@ose3-helper ~]# vgextend VolGroup00  /dev/vdb
  Volume group "VolGroup00" successfully extended

[root@ose3-helper ~]# vgs
  VG         #PV #LV #SN Attr   VSize  VFree
  VolGroup00   2   3   0 wz--n- 17.75g 7.97g
Now I see the 8 GB that I added, as Free.

Resize the docker LV

If you prefer just to extend the volume, this is the command:
[root@ose3-helper ~]# lvextend -l 100%FREE /dev/VolGroup00/docker-pool
  Size of logical volume VolGroup00/docker-pool_tdata changed from 480.00 MiB (15 extents) to 7.75 GiB (248 extents).
  Logical volume docker-pool successfully resized

[root@ose3-helper ~]# lvs
  LV          VG         Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  LogVol00    VolGroup00 -wi-ao---- 7.97g
  LogVol01    VolGroup00 -wi-ao---- 1.50g
  docker-pool VolGroup00 twi-a-t--- 7.75g             3.23   0.22

Delete the docker LV and recreate it

As I need to remove the docker LV so it can be recreated through the docker-storage-setup script, I need to stop the process, and remove what it was there:
[root@ose3-helper ~]# systemctl stop docker

[root@ose3-helper ~]# rm -rf /var/lib/docker/*
Now I will remove the docker LV so I can recreate it fully
[root@ose3-helper ~]# lvremove VolGroup00/docker-pool
Do you really want to remove active logical volume docker-pool? [y/n]: y
  Logical volume "docker-pool" successfully removed
And now I will recreate it with the script:
[root@ose3-helper ~]# echo <<EOF > /etc/sysconfig/docker-storage-setup
> SETUP_LVM_THIN_POOL=yes
> EOF

[root@ose3-helper ~]# docker-storage-setup
  Rounding up size to full physical extent 32.00 MiB
  Logical volume "docker-poolmeta" created.
  Logical volume "docker-pool" created.
  WARNING: Converting logical volume VolGroup00/docker-pool and VolGroup00/docker-poolmeta to pool's data and metadata volumes.
  THIS WILL DESTROY CONTENT OF LOGICAL VOLUME (filesystem etc.)
  Converted VolGroup00/docker-pool to thin pool.
  Logical volume "docker-pool" changed.

[root@ose3-helper ~]# lvs
  LV          VG         Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  LogVol00    VolGroup00 -wi-ao---- 7.97g
  LogVol01    VolGroup00 -wi-ao---- 1.50g
  docker-pool VolGroup00 twi-a-t--- 4.94g             0.00   0.11

It seems like this second option, as it uses thin provisioning, it doesn’t assign the whole available space to the docker-pool.

6 comentarios:

sdodson dijo...

Any idea how you ended up with free space on the rootvg to start with?

pou dijo...

Hi Scott,
Not sure what you mean on how I ended with free space on the rootvg to start with.

I used a Vagrant box that I pulled down from Red Hat and partitioning was already there, so I guess that was on initial partitioning.

This is what I can see in the anaconda-ks.cfg for that Vagrant box.

---------------------------
# Partition clearing information
clearpart --all --drives=vda
# Disk partitioning information
part pv.59 --fstype="lvmpv" --ondisk=vda --size=10038
part /boot --fstype="ext4" --ondisk=vda --size=200
volgroup VolGroup00 --pesize=32768 pv.59
logvol swap --fstype="swap" --grow --maxsize=1536 --size=768 --name=LogVol01 --vgname=VolGroup00
logvol / --fstype="ext4" --grow --size=1024 --name=LogVol00 --vgname=VolGroup00
---------------------------

Not sure if this answers your question. If not, please be more specific, as I'm a middleware guy, you need to talk easier to me ;-)

sdodson dijo...

Thanks, the kickstart config you provided makes sense.

Buddy dijo...

Have you automated that using vagrant?

pou dijo...

Buddy,
Yes, it is automated, but not fully documented yet :-(
https://github.com/jorgemoralespou/jboss-virtual-environments/tree/master/vagrant-vms/openshift3

You'll require the base box, and active subscriptions for RHEL in order to install Openshift v3. Also, I think it is workng only for libvirt, so maybe it will not work for the MacOS X users :-(

I'll try to document everything soon.

Dávid Balakirev dijo...

This is the best resource I have found on the topic. I managed to setup my docker volume fine with your help. Thanks!!!