If it was simple possession, he'd probably get Proposition 36 again. Possession of meth, Health & Safety Code 11377, is a "wobbler" that can be charged as a misdemeanor, with a maximum of a year in jail, or a felony with a potential for as much as three years in prison.
However, an ounce of crank is a huge amount for a user (about 280 average doses), so he may be charged with Health & Safety Code 11379, transportation, and 11378, possession for sale. Both are felonies. Transportation has a maximum prison sentence of four years, and possession for sale is three years. (He can't be sentenced for both based on the same dope.) He might also get probation, with up to a year in jail.
Based on what you've written, he doesn't have to worry about the Three Strikes law. In order to qualify as a strike, the prior conviction has to be one of the serious felonies listed in Penal Code 1192.7(c) or a violent felony in Penal Code 667.5(c). Being under the influence of a controlled substance, Health & Safety Code 11550, is a misdemeanor.
One ounce of meth in Santa Clara County will be charged as possession for sales. Even though he will not be eligible for prop 36, this is still not a strike. Strikes are reserved for serious and violent felonies. The charge is punishable by a prison commitment for up to three years and being on probation does not help. A good defense attorney should be able to keep him from going to prison based upon those facts. I am curious about the reason for the stop and whether he was on searchable probation.