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Currently nova doesn't limit the disk IO bandwidth in copy_image() method while creating a new instance, so the other instances on this host may be affected by this high disk IO consuming operation, and some time-sensitive business(e.g RDS instance with heartbeat) may be switched between master and slave.

So can we use the `rsync --bwlimit=${bandwidth} src dst` command instead of `cp src dst` while copy_image in create_image() of libvirt driver, the remote image copy operation also can be limited by `rsync --bwlimit=${bandwidth}` or `scp -l=${bandwidth}`, this parameter ${bandwidth} can be a new configuration in nova.conf which allow cloud admin to config it, it's default value is 0 which means no limitation, then the instances on this host will be not affected while a new instance with not cached image is creating.

the example codes:
nova/virt/libvit/utils.py:
diff --git a/nova/virt/libvirt/utils.py b/nova/virt/libvirt/utils.py
index e926d3d..5d7c935 100644
--- a/nova/virt/libvirt/utils.py
+++ b/nova/virt/libvirt/utils.py
@@ -473,7 +473,10 @@ def copy_image(src, dest, host=None):
         # sparse files.  I.E. holes will not be written to DEST,
         # rather recreated efficiently.  In addition, since
         # coreutils 8.11, holes can be read efficiently too.
-        execute('cp', src, dest)
+        if CONF.mbps_in_copy_image > 0:
+            execute('rsync', '--bwlimit=%s' % CONF.mbps_in_copy_image * 1024, src, dest)
+        else:
+            execute('cp', src, dest)
     else:
         dest = "%s:%s" % (host, dest)
         # Try rsync first as that can compress and create sparse dest files.
@@ -484,11 +487,22 @@ def copy_image(src, dest, host=None):
             # Do a relatively light weight test first, so that we
             # can fall back to scp, without having run out of space
             # on the destination for example.
-            execute('rsync', '--sparse', '--compress', '--dry-run', src, dest)
+            if CONF.mbps_in_copy_image > 0:
+                execute('rsync', '--sparse', '--compress', '--dry-run',
+                        '--bwlimit=%s' % CONF.mbps_in_copy_image * 1024, src, dest)
+            else:
+                execute('rsync', '--sparse', '--compress', '--dry-run', src, dest)
         except processutils.ProcessExecutionError:
-            execute('scp', src, dest)
+            if CONF.mbps_in_copy_image > 0:
+                execute('scp', '-l', '%s' % CONF.mbps_in_copy_image * 1024 * 8, src, dest)
+            else:
+                execute('scp', src, dest)
         else:
-            execute('rsync', '--sparse', '--compress', src, dest)
+            if CONF.mbps_in_copy_image > 0:
+                execute('rsync', '--sparse', '--compress',
+                        '--bwlimit=%s' % CONF.mbps_in_copy_image * 1024, src, dest)
+            else:
+                execute('rsync', '--sparse', '--compress', src, dest)


2014-02-14



Wangpan
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