Commit d3b06210 authored by Bernardo Dal Seno's avatar Bernardo Dal Seno

Update design doc for partitioned Ganeti

PVs don't need to be marked as unallocatable, as the code will ignore
partially used PVs. exclusive_storage made a node parameter.
Signed-off-by: default avatarBernardo Dal Seno <bdalseno@google.com>
Reviewed-by: default avatarIustin Pop <iustin@google.com>
parent 712da82f
......@@ -27,12 +27,13 @@ all possible sources of it.
Exclusive use of disks
----------------------
``exclusive_storage`` is a configuration flag at node-group and cluster
level. When it's enabled, Ganeti will allocate entire disks to
instances. Though it's possible to think of ways of doing something
similar for other storage back-ends, this design targets only ``plain``
and ``drbd``. The name is generic enough in case the feature will be
extended to other back-ends.
``exclusive_storage`` is a new node parameter. When it's enabled, Ganeti
will allocate entire disks to instances. Though it's possible to think
of ways of doing something similar for other storage back-ends, this
design targets only ``plain`` and ``drbd``. The name is generic enough
in case the feature will be extended to other back-ends. The flag value
should be homogeneous within a node-group; ``cluster-verify`` will report
any violation of this condition.
Ganeti will consider each physical volume in the destination volume
group as a host disk (for proper isolation, an administrator should
......@@ -45,12 +46,13 @@ and as part of ``cluster-verify``.
When creating a new disk for an instance, Ganeti will allocate the
minimum number of PVs to hold the disk, and those PVs will be excluded
from the pool of available PVs by marking them as unallocatable; in this
way, PVs won't be shared between instance disks, and any remaining space
won't be used by mistake for anything else. The underlying LV will be
striped, when striping is allowed by the current configuration. Ganeti
will continue to track only the LVs, and query the LVM layer to figure
out which PVs are available and how much space is free.
from the pool of available PVs for further disk creations. The
underlying LV will be striped, when striping is allowed by the current
configuration. Ganeti will continue to track only the LVs, and query the
LVM layer to figure out which PVs are available and how much space is
free. Yet, creation, disk growing, and free-space reporting will ignore
any partially allocated PVs, so that PVs won't be shared between
instance disks.
For compatibility with the DRBD template and to take into account disk
variability, Ganeti will always subtract 2% (this will be a parameter)
......
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