On 2010-01-25 at 08:31 -0600 Mike Gerdts sent off: > You are missing the point. Compression and dedup will make it so that > the blocks in the devices are not overwritten with zeroes. The goal > is to overwrite the blocks so that a back-end storage device or > back-end virtualization platform can recognize that the blocks are not > in use and as such can reclaim the space.
a filesystem that is able to do that fast would have to implement something like unwritten extents. Some days ago I experimented to create and allocate huge files on ZFS ontop of OpenSolaris using fnctl and F_ALLOCSP which is basically the same thing that you want to do when you zero out space. It takes ages because it actually writes zeroes to the disk. A filesystem that knows the concept of unwritten extents finishes the job immediately. There are no real zeros on the disk but the extent is tagged to be unwritten (you get zeros when you read it). Are there any plans to add unwritten extent support into ZFS or any reason why not? Björn _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
