[pve-devel] [PATCH storage] rbd: add support for erasure coded ec pools

[Aaron Lauterer <a.lauterer@proxmox.com>]

The first step is to allocate rbd images correctly.

The metadata objects still need to be stored in a replicated pool, but
by providing the --data-pool parameter on image creation, we can place
the data objects on the erasure coded (EC) pool.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
---
Right now this only this only affects disk image creation and the EC
pool needs to be created manually to test this.

The Ceph blog about EC with RBD + CephFS gives a nice introduction and
the necessary steps to set up such a pool [0].

The steps needed are:

- create EC profile (a 21 profile is only useful for testing purposes in
     a 3 node cluster, not something that should be considered for
     production use!)
# ceph osd erasure-code-profile set ec-21-profile k=2 m=1 crush-failure-domain=host

- create a new pool with that profile
# ceph osd pool create ec21pool erasure ec-21-profile

- allow overwrite
# ceph osd pool set ec21pool allow_ec_overwrites true

- enable application rbd on the pool (the command in the blog seems to
    have gotten the order of parameters a bit wrong here)
# ceph osd pool application enable ec21pool rbd

- add storage configuration
# pvesm add rbd ectest --pool <replicated pool> --data-pool ec21pool

For the replicated pool, either create a new one without adding the PVE
storage config or use a namespace to separate it from the existing pool.

To create a namespace:
# rbd namespace create <pool>/<namespace>

add the '--namespace' parameter in the pvesm add command.

To check if the objects are stored correclty you can run rados:

# rados -p <pool> ls

This should only show metadata objects

# rados -p <ec pool> ls

This should then show only `rbd_data.xxx` objects.
If you configured a namespace, you also need to add the `--namespace`
parameter to the rados command.


[0] https://ceph.io/en/news/blog/2017/new-luminous-erasure-coding-rbd-cephfs/


 PVE/Storage/RBDPlugin.pm | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/PVE/Storage/RBDPlugin.pm b/PVE/Storage/RBDPlugin.pm
index 2607d25..1ea3418 100644
--- a/PVE/Storage/RBDPlugin.pm
+++ b/PVE/Storage/RBDPlugin.pm
@@ -289,6 +289,10 @@ sub properties {
 	    description => "Pool.",
 	    type => 'string',
 	},
+	'data-pool' => {
+	    description => "Data Pool (for erasure coding only)",
+	    type => 'string',
+	},
 	namespace => {
 	    description => "RBD Namespace.",
 	    type => 'string',
@@ -318,6 +322,7 @@ sub options {
 	disable => { optional => 1 },
 	monhost => { optional => 1},
 	pool => { optional => 1 },
+	'data-pool' => { optional => 1 },
 	namespace => { optional => 1 },
 	username => { optional => 1 },
 	content => { optional => 1 },
@@ -516,7 +521,10 @@ sub alloc_image {
 
     $name = $class->find_free_diskname($storeid, $scfg, $vmid) if !$name;
 
-    my $cmd = $rbd_cmd->($scfg, $storeid, 'create', '--image-format' , 2, '--size', int(($size+1023)/1024), $name);
+    my @options = ('create', '--image-format' , 2, '--size', int(($size+1023)/1024));
+    push @options, ('--data-pool', $scfg->{'data-pool'}) if $scfg->{'data-pool'};
+    push @options, $name;
+    my $cmd = $rbd_cmd->($scfg, $storeid, @options);
     run_rbd_command($cmd, errmsg => "rbd create '$name' error");
 
     return $name;
-- 
2.30.2