title: Disk usage when redshift doing vacuum merge?
body: <p>I know redshift split vacuum progress into two stages: sort and merge.</p>
  
  <p>During sorting, the disk usage will not change, but merge stage seems will occupy a lot of free space.</p>
  
  <p>My cluster is 3 nodes of dw2.xlarge, total 480 GB SSD. Before vacuuming, the total disk usage is around 50%.</p>
  
  <p>I'm doing a vacuum on a a table of 81GB, but it failed when trying to do merge, due to disk full error.</p>
  
  <p>I want to know how much space should I reserve for vacuuming a large unsorted table?</p>
  
  <p>I asked this question to redshift support team, but haven't got any reply until now. Does anyone have experience with it?</p>