             bucket    : BLOB_GCLOUD_BUCKET # name of bucket
             limit     : 1000               # copy this many in each batch
             map_limit : 1                  # copy this many at once.
-            throttle  : 1                  # wait this many seconds between uploads
+            throttle  : 0                  # wait this many seconds between uploads
             repeat_until_done_s : 0        # if nonzero, waits this many seconds, then recalls this function until nothing gets uploaded.
             errors    : {}                 # used to accumulate errors
             remove    : false

        opts = defaults opts,
            limit    : 10000     # number of blobs to backup
            path     : required  # path where [timestamp].tar file is placed
            throttle : 1         # wait this many seconds between pulling blobs from database
            repeat_until_done : 0 # if positive keeps re-call'ing this function until no more results to backup (pauses this many seconds between)
            cb    : undefined # cb(err, '[timestamp].tar')
        dbg     = @dbg("backup_blobs_to_tarball(limit=#{opts.limit},path='#{opts.path}')")
        join    = require('path').join

                opts.cb?(err)
            else
                dbg("done")
                if opts.repeat_until_done and to_remove.length == opts.limit 
                    f = () =>
                        @backup_blobs_to_tarball(opts)
                    setTimeout(f, opts.repeat_until_done*1000)
