There's a limit to the number of SCSI special devices (/dev/sdX) which Linux can utilize (see IBM article
But to answer your question more directly let's turn to the Linux Kernel documentation specifically devices.txt
Analyzing that document the Linux kernel 3.12 (which are the links I provided) can support up to 256 disk drives (i.e. SCSI disk devices). The naming starts at sda-sdz and once sdz is reached it wraps around to sdaa-sdaz and so on. The very last possible device in this naming convention is sdiv.
#all possible device names