Merge pull request #3322 from owncloud/docsaddnfs

[docsonly] Documentation about a test running oCIS over NFS.

docs/ocis/storage-backends/dcfsnfs.md

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+---
+title: "Decomposed FS on NFS"
+date: 2020-03-15T16:35:00+01:00
+weight: 30
+geekdocRepo: https://github.com/owncloud/ocis
+geekdocEditPath: edit/master/docs/ocis/storage-backends/
+geekdocFilePath: dcfsnfs.md
+---
+
+{{< toc >}}
+
+oCIS' default storage backend is the Decomposed FS. The Decomposed FS can be set up to run on a NFS share. That way the same storage can be provided over network to other nodes running oCIS.
+
+This document summarizes a few important considerations of the NFS setup and describes a tested setup. The test has not covered concurrent access of data from different nodes yet.
+
+## NFS Server Setup
+
+This document covers the linux kernel NFS server on a standard Linux running on x86_64.
+
+The NFS server needs to be set up in a way that it supports [extended file attributes](https://en.wikipedia.org/wiki/Extended_file_attributes).
+
+Extended attributes are supported by NFS starting with Kernel version 5.9, which means that the server with the NFS server has to run a kernel with that or a higher version number. To check that, run the command `uname -a` on the NFS server and compare the displayed version number.
+
+The NFS server in the test setup was configured with the following line in the config file `/etc/exports`:
+
+`/space/nfstest 192.168.178.0/24(rw,root_squash,async,subtree_check,anonuid=0,anongid=100,all_squash)`
+
+This exports the directory `/space/nfstest` to the internal network with certain options.
+
+Important:
+
+- The share needs to be exported with the `async` option for proper NFS performance.
+
+## NFS Client Mount
+
+The nodes that run oCIS need to mount the NFS storage to a local mount point.
+
+The test setup uses the client mount command: `mount -t nfs -o nfsvers=4 192.168.178.28:/space/nfstest /mnt/ocisdata/`
+
+It sets the NFS version to 4, which is important to support extended attributes.
+
+After successful mounting the storage on the client, it can be checked if the NFS setup really supports extended attributes properly using the following commands.
+
+`setfattr -n user.test -v "xattr test string" ocisdata/foo` to write an extended attribute to a file, and `getfattr -d ocisdata/foo` to list all the attributes a file has set.
+
+{{< hint info >}}
+The NFS server setup can be optimized considering system administrative-, performance- and security options. This is not (yet) covered in this documentation.
+{{< /hint >}}
+
+## oCIS Start using the NFS Share
+
+The oCIS server can be instructed to set up the decomposed FS at a certain path by setting the environment variable `OCIS_BASE_DATA_PATH`.
+
+The test setup started an oCIS tech preview single binary release using this start command:
+
+```
+OCIS_BASE_DATA_PATH=/mnt/ocisdata/ OCIS_LOG_LEVEL=debug OCIS_INSECURE=true PROXY_HTTP_ADDR=0.0.0.0:9200 OCIS_URL=https://hostname:9200 ./ocis-1.18.0-linux-amd64 server
+```
+
+This starts oCIS and a decomposed FS skeleton file system structure is set up on the NFS share.
+
+The oCIS instance is passing a smoke test.
+
+