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Update repo README.md for quorum slots

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Update the example configuration in the README to specify the quorum
slots in mkfs arguments and mount options.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-02-08 13:02:41 -08:00
parent d53350f9f1
commit 090646aaeb
1 changed files with 22 additions and 11 deletions
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33
README.md
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@@ -65,8 +65,13 @@ The steps for getting scoutfs mounted and operational are:
2. Make a new filesystem on the devices with the userspace utilities
3. Mount the devices on all the nodes
In this example we run all of these commands on three nodes. The names
of the block devices are the same on all the nodes.
In this example we use three nodes. The names of the block devices are
the same on all the nodes. Two of the nodes will be quorum members. A
majority of quorum members must be mounted to elect a leader to run a
server that all the mounts connect to. It should be noted that two
quorum members results in a majority of one, each member itself, so
split brain elections are possible but so unlikely that it's fine for a
demonstration.
1. Get the Kernel Module and Userspace Binaries
@@ -88,24 +93,30 @@ of the block devices are the same on all the nodes.
alias scoutfs=$PWD/scoutfs/utils/src/scoutfs
```
2. Make a New Filesystem (**destroys contents, no questions asked**)
2. Make a New Filesystem (**destroys contents**)
We specify that two of our three nodes must be present to form a
quorum for the system to function.
We specify quorum slots with the addresses of each of the quorum
member nodes, the metadata device, and the data device.
```shell
scoutfs mkfs -Q 2 /dev/meta_dev /dev/data_dev
scoutfs mkfs -Q 0,$NODE0_ADDR,12345 -Q 1,$NODE1_ADDR,12345 /dev/meta_dev /dev/data_dev
```
3. Mount the Filesystem
Each mounting node provides its local IP address on which it will run
an internal server for the other mounts if it is elected the leader by
the quorum.
First, mount each of the quorum nodes so that they can elect and
start a server for the remaining node to connect to. The slot numbers
were specified with the leading "0,..." and "1,..." in the mkfs options
above.
```shell
mkdir /mnt/scoutfs
mount -t scoutfs -o server_addr=$NODE_ADDR,metadev_path=/dev/meta_dev /dev/data_dev /mnt/scoutfs
mount -t scoutfs -o quorum_slot_nr=$SLOT_NR,metadev_path=/dev/meta_dev /dev/data_dev /mnt/scoutfs
```
Then mount the remaining node which can now connect to the running server.
```shell
mount -t scoutfs -o metadev_path=/dev/meta_dev /dev/data_dev /mnt/scoutfs
```
4. For Kicks, Observe the Metadata Change Index