The initial overhead is fairly small (extra hard link for each file).
After that, the overhead grows as you delete the files (thus its blocks) that existed before the upgrade.. since the physical files for blocks are deleted only after you finalize.
So the overhead == (the blocks that got deleted after the upgrade). Raghu. Stu Hood wrote:
Hey gang, We're preparing to upgrade our cluster from Hadoop 0.15.3 to 0.18.3. How much disk usage overhead can we expect from the block conversion before we finalize the upgrade? In the worst case, will the upgrade cause our disk usage to double? Thanks, Stu Hood Search Team Technical Lead Email & Apps Division, Rackspace Hosting
