lstart column – the starting page number in the database of this allocation unit. Each database starts at logical address 0. If additional allocations have been made for a database, as in the case of dbid 7, the lstart column reflects this.
size column – the number of contiguous pages that are assigned to the same database. The ending logical address of this portion of the database can be determined by adding the values in lstart and size.
vstart column – the address where the piece assigned to this database begins. The upper 4 bits store the virtual device number (vdevno), and the lower 4 bits store the virtual block number. (To obtain the virtual device number, divide sysusages.vstart or sysdevices.low by 16,777,216, which is 224.) The value in vstart identifies which database device contains the page number of the database, because it falls between the values in the low and high columns of sysdevices for the database device in question.
