Design correct reporting of storage free space

This is a long standing bug in Ganeti. Add a small design on how we plan
to fix this for Ganeti 2.7.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>

diff --git a/Makefile.am b/Makefile.am
index fc3a522..871b471 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -402,6 +402,7 @@ docinput = \
        doc/design-virtual-clusters.rst \
        doc/design-x509-ca.rst \
        doc/design-hroller.rst \
+       doc/design-storagespace.rst \
        doc/devnotes.rst \
        doc/glossary.rst \
        doc/hooks.rst \

diff --git a/doc/design-draft.rst b/doc/design-draft.rst
index c18469b..9dd2dfc 100644 (file)
--- a/doc/design-draft.rst
+++ b/doc/design-draft.rst
@@ -16,6 +16,7 @@ Design document drafts
    design-partitioned.rst
    design-monitoring-agent.rst
    design-hroller.rst
+   design-storagespace.rst
 
 .. vim: set textwidth=72 :
 .. Local Variables:

diff --git a/doc/design-storagespace.rst b/doc/design-storagespace.rst
new file mode 100644 (file)
index 0000000..919479f
--- /dev/null
+++ b/doc/design-storagespace.rst
@@ -0,0 +1,116 @@
+============================
+Storage free space reporting
+============================
+
+.. contents:: :depth: 4
+
+Background
+==========
+
+Currently Space reporting is broken for all storage types except drbd or
+lvm (plain). This design looks at the root causes and proposes a way to
+fix it.
+
+Proposed changes
+================
+
+The changes below will streamline Ganeti to properly support
+interaction with different storage types.
+
+Configuration changes
+---------------------
+
+Each storage type will have a new "pools" parameter added (type list of
+strings). This will be list of vgs for plain and drbd (note that we make
+no distinction at this level between allowed vgs and metavgs), the list
+of rados pools for rados, or the storage directory for file and
+sharedfile. The parameters already present in the cluster config object
+will be moved to the storage parameters.
+
+Since currently file and sharedfile only support a single directory this
+list will be limited to one. In the future if we'll have support for
+more directories, or for per-nodegroup directories this can be changed.
+
+Note that these are just "mechanisms" parameters that define which
+storage pools the cluster can use. Further filtering about what's
+allowed can go in the ipolicy, but these changes are not covered in this
+design doc.
+
+Since the ipolicy currently has a list of enabled storage types, we'll
+use that to decide which storage type is the default, and to self-select
+it for new instance creations, and reporting.
+
+Enabling/disabling of storage types at ``./configure`` time will be
+eventually removed.
+
+RPC changes
+-----------
+
+The noded RPC call that reports node storage space will be changed to
+accept a list of <method>,<key> string tuples. For each of them it will
+report the free amount of space found on storage <key> as known by the
+requested method. Methods are for example ``lvm``, ``filesystem``,
+``rados``, and the key would be a volume group name in the case of lvm,
+a directory name for the filesystem and a rados pool name, for
+rados_pool.
+
+Masterd will know (through a constant map) which storage type uses which
+method for storage calculation (i.e. ``plain`` and ``drbd`` use ``lvm``,
+``file`` and ``sharedfile`` use ``filesystem``, etc) and query the one
+needed (or all of the needed ones).
+
+Note that for file and sharedfile the node knows which directories are
+allowed and won't allow any other directory to be queried for security
+reasons. The actual path still needs to be passed to distinguish the
+two, as the method will be the same for both.
+
+These calculations will be implemented in the node storage system
+(currently lib/storage.py) but querying will still happen through the
+``node info`` call, to avoid requiring an extra RPC each time.
+
+Ganeti reporting
+----------------
+
+``gnt-node list`` will by default report information just about the
+default storage type. It will be possible to add fields to ask about
+other ones, if they're enabled.
+
+``gnt-node info`` will report information about all enabled storage
+types, without querying them (just say which ones are supported
+according to the cluster configuration).
+
+``gnt-node list-storage`` will change to report information about all
+available storage pools in each storage type. An extra flag will be
+added to filter by storage pool name (alternatively we can implement
+this by allowing to query by a list of ``type:pool`` string tuples to
+have a more comprehensive filter).
+
+
+Allocator changes
+-----------------
+
+The iallocator protocol doesn't need to change: since we know which
+storage type an instance has, we'll pass only the "free" value for that
+storage type to the iallocator, when asking for an allocation to be
+made. Note that for DRBD nowadays we ignore the case when vg and metavg
+are different, and we only consider the main VG. Fixing this is outside
+the scope of this design.
+
+Rebalancing changes
+-------------------
+
+Hbal will not need changes, as it handles it already. We don't forecast
+any changes needed to it.
+
+Space reporting changes
+-----------------------
+
+Hspace will by default report by assuming the allocation will happen on
+the default storage for the cluster/nodegroup. An option will be added
+to manually specify a different storage.
+
+.. vim: set textwidth=72 :
+.. Local Variables:
+.. mode: rst
+.. fill-column: 72
+.. End: