I have no objections, but think it could look better if made an array.

Ok, so, the problem with making it an array is that bio_cmd flags are defined like this:

#define BIO_READ 0x01 /* Read I/O data */
#define BIO_WRITE 0x02 /* Write I/O data */
#define BIO_DELETE 0x04 /* TRIM or free blocks, i.e. mark as unused */
#define BIO_GETATTR 0x08 /* Get GEOM attributes of object */
#define BIO_FLUSH 0x10 /* Commit outstanding I/O now */
#define BIO_CMD0 0x20 /* Available for local hacks */
#define BIO_CMD1 0x40 /* Available for local hacks */
#define BIO_CMD2 0x80 /* Available for local hacks */

Ie, it's not an enum, so we can't just do "sc->sc_cmds[bp->bio_cmd]++". And without it, making it an array doesn't really improve much.