ALTER PROC [dbo].[Proc_A_Update_X] @ID char(32) , @textBlock text as 
update A set textBlock = null  
    where ID=@ID 
DECLARE @ptrval varbinary(16) 
SELECT @ptrval = TEXTPTR(textBlock)  
FROM A
WHERE ID=@fID

WRITETEXT A.textBlock  @ptrval with log @textBlock 

ALTER Trigger [dbo].[Tri_A_InsteadUPdate] on [dbo].[A] instead of update
as
declare @ID char(31)         
declare @TxtBlock nvarchar(max)
begin
if update(X)
begin
    select @TxtBlock = inserted.X,@ID= inserted.ID from inserted
    if (select count(*) from B where ID= @ID) = 0
    begin
        insert into B(ID, x) values(@ID,@TxtBlock)
    end
    else
    begin
        UPdate B set X=@TxtBlock where ID=@ID
    end
end
end