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Merge pull request #22968 from mbentley/fix-dm-docs 

Fixed lost thin pool devicemapper docs
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Vincent Demeester 2016-05-25 16:40:52 +02:00
parent 2a4b4a8133 0b8ea4387a
commit 5bd6067b85
2 changed files with 134 additions and 94 deletions
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docs/userguide/storagedriver/device-mapper-driver.md
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@ -212,7 +212,7 @@ a `direct-lvm` configuration.
> and have images you want to keep, `push` them Docker Hub or your private > and have images you want to keep, `push` them Docker Hub or your private
> Docker Trusted Registry before attempting this procedure. > Docker Trusted Registry before attempting this procedure.
The procedure below will create a 90GB data volume and 4GB metadata volume to The procedure below will create a logical volume configured as a thin pool to
use as backing for the storage pool. It assumes that you have a spare block use as backing for the storage pool. It assumes that you have a spare block
device at `/dev/xvdf` with enough free space to complete the task. The device device at `/dev/xvdf` with enough free space to complete the task. The device
identifier and volume sizes may be be different in your environment and you identifier and volume sizes may be be different in your environment and you
@ -221,106 +221,146 @@ assumes that the Docker daemon is in the `stopped` state.
1. Log in to the Docker host you want to configure and stop the Docker daemon. 1. Log in to the Docker host you want to configure and stop the Docker daemon.
2. If it exists, delete your existing image store by removing the 2. Install the LVM2 package.
`/var/lib/docker` directory. The LVM2 package includes the userspace toolset that provides logical volume
management facilities on linux.
3. Create a physical volume replacing `/dev/xvdf` with your block device.
```bash ```bash
$ sudo rm -rf /var/lib/docker $ pvcreate /dev/xvdf
``` ```
3. Create an LVM physical volume (PV) on your spare block device using the 4. Create a 'docker' volume group.
`pvcreate` command.
```bash ```bash
$ sudo pvcreate /dev/xvdf $ vgcreate docker /dev/xvdf
Physical volume `/dev/xvdf` successfully created
``` ```
The device identifier may be different on your system. Remember to substitute 5. Create a thin pool named `thinpool`.
your value in the command above. If your host is running on AWS EC2, you may
need to install `lvm2` and <a href="http://goo.gl/Q5pUwG"
target="_blank">attach an EBS device</a> to use this procedure.
4. Create a new volume group (VG) called `vg-docker` using the PV created in In this example, the data logical is 95% of the 'docker' volume group size.
the previous step. Leaving this free space allows for auto expanding of either the data or
metadata if space runs low as a temporary stopgap.
```bash ```bash
$ sudo vgcreate vg-docker /dev/xvdf $ lvcreate --wipesignatures y -n thinpool docker -l 95%VG
Volume group `vg-docker` successfully created $ lvcreate --wipesignatures y -n thinpoolmeta docker -l 1%VG
``` ```
5. Create a new 90GB logical volume (LV) called `data` from space in the 6. Convert the pool to a thin pool.
`vg-docker` volume group.
```bash ```bash
$ sudo lvcreate -L 90G -n data vg-docker $ lvconvert -y --zero n -c 512K --thinpool docker/thinpool --poolmetadata docker/thinpoolmeta
Logical volume `data` created.
``` ```
The command creates an LVM logical volume called `data` and an associated 7. Configure autoextension of thin pools via an `lvm` profile.
block device file at `/dev/vg-docker/data`. In a later step, you instruct the
`devicemapper` storage driver to use this block device to store image and
container data.
If you receive a signature detection warning, make sure you are working on
the correct devices before continuing. Signature warnings indicate that the
device you're working on is currently in use by LVM or has been used by LVM in
the past.
6. Create a new logical volume (LV) called `metadata` from space in the
`vg-docker` volume group.
```bash ```bash
$ sudo lvcreate -L 4G -n metadata vg-docker $ vi /etc/lvm/profile/docker-thinpool.profile
Logical volume `metadata` created.
``` ```
This creates an LVM logical volume called `metadata` and an associated 8. Specify 'thin_pool_autoextend_threshold' value.
block device file at `/dev/vg-docker/metadata`. In the next step you instruct
the `devicemapper` storage driver to use this block device to store image and
container metadata.
7. Start the Docker daemon with the `devicemapper` storage driver and the The value should be the percentage of space used before `lvm` attempts
`--storage-opt` flags. to autoextend the available space (100 = disabled).
The `data` and `metadata` devices that you pass to the `--storage-opt` ```
options were created in the previous steps. thin_pool_autoextend_threshold = 80
```
9. Modify the `thin_pool_autoextend_percent` for when thin pool autoextension occurs.
The value's setting is the perentage of space to increase the thin pool (100 =
disabled)
```
thin_pool_autoextend_percent = 20
```
10. Check your work, your `docker-thinpool.profile` file should appear similar to the following:
An example `/etc/lvm/profile/docker-thinpool.profile` file:
```
activation {
thin_pool_autoextend_threshold=80
thin_pool_autoextend_percent=20
}
```
11. Apply your new lvm profile
```bash ```bash
$ sudo docker daemon --storage-driver=devicemapper --storage-opt dm.datadev=/dev/vg-docker/data --storage-opt dm.metadatadev=/dev/vg-docker/metadata & $ lvchange --metadataprofile docker-thinpool docker/thinpool
[1] 2163
[root@ip-10-0-0-75 centos]# INFO[0000] Listening for HTTP on unix (/var/run/docker.sock)
INFO[0027] Option DefaultDriver: bridge
INFO[0027] Option DefaultNetwork: bridge
<-- output truncated -->
INFO[0027] Daemon has completed initialization
INFO[0027] Docker daemon commit=1b09a95 graphdriver=aufs version=1.11.0-dev
``` ```
It is also possible to set the `--storage-driver` and `--storage-opt` flags 12. Verify the `lv` is monitored.
in the Docker config file and start the daemon normally using the `service` or
`systemd` commands.
8. Use the `docker info` command to verify that the daemon is using `data` and
`metadata` devices you created.
```bash ```bash
$ sudo docker info $ lvs -o+seg_monitor
INFO[0180] GET /v1.20/info
Containers: 0
Images: 0
Storage Driver: devicemapper
Pool Name: docker-202:1-1032-pool
Pool Blocksize: 65.54 kB
Backing Filesystem: xfs
Data file: /dev/vg-docker/data
Metadata file: /dev/vg-docker/metadata
[...]
``` ```
The output of the command above shows the storage driver as `devicemapper`. 13. If the Docker daemon was previously started, clear your graph driver directory.
The last two lines also confirm that the correct devices are being used for
the `Data file` and the `Metadata file`. Clearing your graph driver removes any images, containers, and volumes in your
Docker installation.
```bash
$ rm -rf /var/lib/docker/*
```
14. Configure the Docker daemon with specific devicemapper options.
There are two ways to do this. You can set options on the commmand line if you start the daemon there:
```bash
--storage-driver=devicemapper --storage-opt=dm.thinpooldev=/dev/mapper/docker-thinpool --storage-opt dm.use_deferred_removal=true
```
You can also set them for startup in the `daemon.json` configuration, for example:
```json
{
"storage-driver": "devicemapper",
"storage-opts": [
"dm.thinpooldev=/dev/mapper/docker-thinpool",
"dm.use_deferred_removal=true"
]
}
```
15. If using systemd and modifying the daemon configuration via unit or drop-in file, reload systemd to scan for changes.
```bash
$ systemctl daemon-reload
```
16. Start the Docker daemon.
```bash
$ systemctl start docker
```
After you start the Docker daemon, ensure you monitor your thin pool and volume
group free space. While the volume group will auto-extend, it can still fill
up. To monitor logical volumes, use `lvs` without options or `lvs -a` to see tha
data and metadata sizes. To monitor volume group free space, use the `vgs` command.
Logs can show the auto-extension of the thin pool when it hits the threshold, to
view the logs use:
```bash
$ journalctl -fu dm-event.service
```
If you run into repeated problems with thin pool, you can use the
`dm.min_free_space` option to tune the Engine behavior. This value ensures that
operations fail with a warning when the free space is at or near the minimum.
For information, see <a
href="../../../reference/commandline/dockerd/#storage-driver-options"
target="_blank">the storage driver options in the Engine daemon reference</a>.
### Examine devicemapper structures on the host ### Examine devicemapper structures on the host
@ -342,7 +382,7 @@ xvdf 202:80 0 10G 0 disk
The diagram below shows the image from prior examples updated with the detail The diagram below shows the image from prior examples updated with the detail
from the `lsblk` command above. from the `lsblk` command above.
![](http://farm1.staticflickr.com/703/22116692899_0471e5e160_b.jpg) ![](images/lsblk-diagram.jpg)
In the diagram, the pool is named `Docker-202:1-1032-pool` and spans the `data` In the diagram, the pool is named `Docker-202:1-1032-pool` and spans the `data`
and `metadata` devices created earlier. The `devicemapper` constructs the pool and `metadata` devices created earlier. The `devicemapper` constructs the pool
@ -427,12 +467,10 @@ The `Data Space` values show that the pool is 100GB total. This example extends
3. Verify the file size changed. 3. Verify the file size changed.
```bash ```bash
$ sudo ls -al /var/lib/docker/devicemapper/devicemapper/ $ sudo ls -lh /var/lib/docker/devicemapper/devicemapper/
total 1175492 total 1.2G
drwx------ 2 root root 4096 Mar 29 02:45 . -rw------- 1 root root 200G Apr 14 08:47 data
drwx------ 5 root root 4096 Mar 29 02:48 .. -rw------- 1 root root 2.0G Apr 19 13:27 metadata
-rw------- 1 root root 214748364800 Mar 31 11:20 data
-rw------- 1 root root 2147483648 Mar 31 11:17 metadata
``` ```
4. Reload data loop device 4. Reload data loop device
@ -450,7 +488,8 @@ The `Data Space` values show that the pool is 100GB total. This example extends
a. Get the pool name first. a. Get the pool name first.
```bash ```bash
$ sudo dmsetup status docker-8:1-123141-pool: 0 209715200 thin-pool 91 $ sudo dmsetup status | grep pool
docker-8:1-123141-pool: 0 209715200 thin-pool 91
422/524288 18338/1638400 - rw discard_passdown queue_if_no_space - 422/524288 18338/1638400 - rw discard_passdown queue_if_no_space -
``` ```
@ -469,6 +508,7 @@ The `Data Space` values show that the pool is 100GB total. This example extends
reflect the new number of 512 byte sectors in the disk. For example, as the reflect the new number of 512 byte sectors in the disk. For example, as the
new loop size is 200GB, change the second number to 419430400. new loop size is 200GB, change the second number to 419430400.
d. Reload the thin pool with the new sector number d. Reload the thin pool with the new sector number
```bash ```bash
@ -533,7 +573,7 @@ disk partition.
c. Calculate the real total sectors of the thin pool now. we can use `blockdev` to get the real size of data lv. c. Calculate the real total sectors of the thin pool now. we can use `blockdev` to get the real size of data lv.
Change the second number of the table info (i.e. the disk end sector) to Change the second number of the table info (i.e. the number of sectors) to
reflect the new number of 512 byte sectors in the disk. For example, as the reflect the new number of 512 byte sectors in the disk. For example, as the
new data `lv` size is `264132100096` bytes, change the second number to new data `lv` size is `264132100096` bytes, change the second number to
`515883008`. `515883008`.
@ -592,8 +632,8 @@ There are several other things that impact the performance of the
- **The mode.** The default mode for Docker running the `devicemapper` storage - **The mode.** The default mode for Docker running the `devicemapper` storage
driver is `loop-lvm`. This mode uses sparse files and suffers from poor driver is `loop-lvm`. This mode uses sparse files and suffers from poor
performance. It is **not recommended for production**. The recommended mode performance. It is **not recommended for production**. The recommended mode for
for production environments is `direct-lvm` where the storage driver writes production environments is `direct-lvm` where the storage driver writes
directly to raw block devices. directly to raw block devices.
- **High speed storage.** For best performance you should place the `Data file` - **High speed storage.** For best performance you should place the `Data file`
@ -601,10 +641,10 @@ There are several other things that impact the performance of the
attached storage or from a SAN or NAS array. attached storage or from a SAN or NAS array.
- **Memory usage.** `devicemapper` is not the most memory efficient Docker - **Memory usage.** `devicemapper` is not the most memory efficient Docker
storage driver. Launching *n* copies of the same container loads *n* copies storage driver. Launching *n* copies of the same container loads *n* copies of
of its files into memory. This can have a memory impact on your Docker host. its files into memory. This can have a memory impact on your Docker host. As a
As a result, the `devicemapper` storage driver may not be the best choice for result, the `devicemapper` storage driver may not be the best choice for PaaS
PaaS and other high density use cases. and other high density use cases.
One final point, data volumes provide the best and most predictable One final point, data volumes provide the best and most predictable
performance. This is because they bypass the storage driver and do not incur performance. This is because they bypass the storage driver and do not incur

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