title: what is mongodb archive format?
body: <p>I've backed up some mongoDBs using their archive option, but I can't simply untar them. When I go through some steps to decompress the data it looks like the archive is the whole DB in one big file.
  I wanted to get at the files for the individual collections.
  Is there a way to do that?</p>
  
  <pre><code>$ tar -xvf valk.archive
  tar: Unrecognized archive format
  tar: Error exit delayed from previous errors.
  $ file valk.archive
  valk.archive: gzip compressed data, original size 13953183
  $ gunzip valk.archive
  gunzip: valk.archive: unknown suffix -- ignored
  $ unzip valk.archive
  Archive:  valk.archive
    End-of-central-directory signature not found.  Either this file is not
    a zipfile, or it constitutes one disk of a multi-part archive.  In the
    latter case the central directory and zipfile comment will be found on
    the last disk(s) of this archive.
  unzip:  cannot find zipfile directory in one of valk.archive or
          valk.archive.zip, and cannot find valk.archive.ZIP, period.
  $ mv valk.zip valk.gz
  $ gunzip valk.gz
  $ open .
  $ tar -xvf valk
  tar: Unrecognized archive format
  tar: Error exit delayed from previous errors.
  $ head valk
  TemplateDatametadata�{"options":{},"indexes":[{"v":2,"key":{"_id":1},"name":"_id_","ns":"valk.TemplateData"}],"uuid":"f52402b5aba24856b072d57cc3e46a72"}size-dbvalkcollectioMetricsmetadata�{"options":{"capped":true,"size":10485760,"max":1000000},"indexes":[{"v":2,"key":{"_id":1},"name":"_id_","ns":"valk.Metrics"},{"v":2,"key":{"openid":1},"name":"openid_1","ns":"valk.Metrics"}],"uuid":"43d92ff01815432c95dac5a2e05a64c0"}size�dbvalkcollection
  AppConfigmetadata�{"options":{},"indexes":[{"v":2,"key":{"_id":1},"name":"_id_","ns":"valk.AppConfig"}],"uuid":"df633b0a43184de38e8b8ea7489cda3e"}size�dbvalkcollecMinibotZonesmetadata�{"options":{},"indexes":[{"v":2,"key":{"_id":1},"name":"_id_","ns":"valk.MinibotZones"}],"uuid":"095bbac0d17640be9e27dffe681b7d83"}size�dbvalkcollection    ChatLogsmetadataQ{"options":{"capped":true,"size":104857600,"max":10000000},"indexes":[{"v":2,"key":{"_id":1},"name":"_id_","ns":"valk.ChatLogs"},{"v":2,"key":{"openid":1,"createdAt":1},"name":"openid_1_createdAt_1","ns":"valk.ChatLogs"},{"v":2,"key":{"createdAt":1},"name":"createdAt_1","ns":"valk.ChatLogs"}],"uuid":"70586c82b3ae42cf8d9c47ad339ea55b"}size�dbvalkcollection
  </code></pre>