 // case 4: truncate to 1.5 blocks
    // all the blocks are in snapshot. truncate need to allocate a new block
    // diff should be +BLOCKSIZE
 // case 4: truncate to 1.5 blocks
    // all the blocks are in snapshot. truncate need to allocate a new block
    // diff should be +BLOCKSIZE | TestTruncateQuotaUpdate.java