Doc for GlusterFS Ganeti Support

This patch adds a design document for introducing GlusterFS Support in Ganeti.

Signed-off-by: Weiwei Jia <harryxiyou@gmail.com>
Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>

diff --git a/doc/design-draft.rst b/doc/design-draft.rst
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--- a/doc/design-draft.rst
+++ b/doc/design-draft.rst
@@ -18,6 +18,7 @@ Design document drafts
    design-storagetypes.rst
    design-device-uuid-name.rst
    design-internal-shutdown.rst
+   design-glusterfs-ganeti-support.rst
 
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diff --git a/doc/design-glusterfs-ganeti-support.rst b/doc/design-glusterfs-ganeti-support.rst
new file mode 100644 (file)
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+========================
+GlusterFS Ganeti support
+========================
+
+This document describes the plan for adding GlusterFS support inside Ganeti.
+
+.. contents:: :depth: 4
+.. highlight:: shell-example
+
+Objective
+=========
+
+The aim is to let Ganeti support GlusterFS as one of its backend storage.
+This includes three aspects to finish:
+
+- Add Gluster as a storage backend.
+- Make sure Ganeti VMs can use GlusterFS backends in userspace mode (for
+  newer QEMU/KVM which has this support) and otherwise, if possible, through
+  some kernel exported block device.
+- Make sure Ganeti can configure GlusterFS by itself, by just joining
+  storage space on new nodes to a GlusterFS nodes pool. Note that this
+  may need another design document that explains how it interacts with
+  storage pools, and that the node might or might not host VMs as well.
+
+Background
+==========
+
+There are two possible ways to implement "GlusterFS Ganeti Support". One is
+GlusterFS as one of external backend storage, the other one is realizing
+GlusterFS inside Ganeti, that is, as a new disk type for Ganeti. The benefit
+of the latter one is that it would not be opaque but fully supported and
+integrated in Ganeti, which would not need to add infrastructures for
+testing/QAing and such. Having it internal we can also provide a monitoring
+agent for it and more visibility into what's going on. For these reasons,
+GlusterFS support will be added directly inside Ganeti.
+
+Implementation Plan
+===================
+
+Ganeti Side
+-----------
+
+To realize an internal storage backend for Ganeti, one should realize
+BlockDev class in `ganeti/lib/storage/base.py` that is a specific
+class including create, remove and such. These functions should be
+realized in `ganeti/lib/storage/bdev.py`. Actually, the differences
+between implementing inside and outside (external) Ganeti are how to
+finish these functions in BlockDev class and how to combine with Ganeti
+itself. The internal implementation is not based on external scripts
+and combines with Ganeti in a more compact way. RBD patches may be a
+good reference here. Adding a backend storage steps are as follows:
+
+- Implement the BlockDev interface in bdev.py.
+- Add the logic in cmdlib (eg, migration, verify).
+- Add the new storage type name to constants.
+- Modify objects.Disk to support GlusterFS storage type.
+- The implementation will be performed similarly to the RBD one (see
+  commit 7181fba).
+
+GlusterFS side
+--------------
+
+GlusterFS is a distributed file system implemented in user space.
+The way to access GlusterFS namespace is via FUSE based Gluster native
+client except NFS and CIFS. The efficiency of this way is lower because
+the data would be pass the kernel space and then come to user space.
+Now, there are two specific enhancements:
+
+- A new library called libgfapi is now available as part of GlusterFS
+  that provides POSIX-like C APIs for accessing Gluster volumes.
+  libgfapi support will be available from GlusterFS-3.4 release.
+- QEMU/KVM (starting from QEMU-1.3) will have GlusterFS block driver that
+  uses libgfapi and hence there is no FUSE overhead any longer when QEMU/KVM
+  works with VM images on Gluster volumes.
+
+There are two possible ways to implement "GlusterFS Ganeti Support" inside
+Ganeti. One is based on libgfapi, which call APIs by libgfapi to realize
+GlusterFS interfaces in bdev.py. The other way is based on QEMU/KVM. Since
+QEMU/KVM has supported for GlusterFS and Ganeti could support for GlusterFS
+by QEMU/KVM. However, the latter way can just let VMs of QEMU/KVM use GlusterFS
+backend storage but other VMs like XEN and such. So the first way is more
+suitable for us.
+
+.. vim: set textwidth=72 :
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+.. mode: rst
+.. fill-column: 72
+.. End: