Hi OnlySandy,  When a host writes to a TDEV then 768KB extents will be allocated as needed. So in your example you allocate some space and then you delete half of the space. The OS deletes the files on the inode list of the filesystem (f.e. when you delete files from an NTFS, Windows puts a $ as the first character) but does not zero out the "actual" data of the files. In order to reclaim the space from the storage , storage needs to find extents that contains only zeroes. So you need to to zero out the space that your data consumed. This is why you need the OS LVM to be able to do this. Such LVM is VxVM 5, VMware or with Win2K8 you can run storeclaim or sdelete.  Rebalance will move around extents to all the TDATs of your pool, to evenly balance the extents on the TDATs based on the Rebalance Variance.  Regards, Kl.
I am very much aware that as an when we write to tdev the pages will get allocated but what will happen if i delete half of data on that tdev ( or from the file system made up of those tdevs) will the pages get deallocate and come back to free pool space or it will not happen until we manually run the Pool Reblanace.  Also even if we unmask any luns from server , we need to destroy them to return the allocated storage back to free pool.
tdev page allocation deallocation