swift-dispersion-tool slow with unreachable storage nodes

If a Swift storage node is down, the swift-dispersion-tool complains that the host is unreachable, for every single object and container that is hosted on that host, multiplied by the retry setting. This causes the tool to run very slowly, and the Nagios check based on this tool then fails.
This patch prevents the swift-dispersion-tool from trying hosts that were found to be down. A useful setting is to set the retries = 1 in /etc/swift/dispersion.conf

--- swift-dispersion-report 2012-10-11 14:19:43.000000000 +0000
+++ swift-dispersion-report.new 2013-01-31 16:38:48.959641951 +0000
@@ -33,6 +33,7 @@
 from swift.common.utils import compute_eta, get_time_units, TRUE_VALUES

+unreachable = []
 unmounted = []
 notfound = []
 json_output = False
@@ -60,6 +61,9 @@
                 stderr.flush()
         if not hasattr(msg_or_exc, 'http_status') or \
                 msg_or_exc.http_status not in (404, 507):
+ ip = prefix.split(':')[0]
+ if ip not in unreachable:
+ unreachable.append(ip)
             print >>stderr, 'ERROR: %s: %s' % (prefix, msg_or_exc)
             stderr.flush()
     return error_log
@@ -85,6 +89,8 @@
     def direct(container, part, nodes):
         found_count = 0
         for node in nodes:
+ if node['ip'] in unreachable:
+ continue
             error_log = get_error_log('%(ip)s:%(port)s/%(device)s' % node)
             try:
                 attempts, _junk = direct_client.retry(
@@ -183,6 +189,8 @@
     def direct(obj, part, nodes):
         found_count = 0
         for node in nodes:
+ if node['ip'] in unreachable:
+ continue
             error_log = get_error_log('%(ip)s:%(port)s/%(device)s' % node)
             try:
                 attempts, _junk = direct_client.retry(