Do I have to actually cast a spell to store it in a Glyph of Warding?

Question

From the PFSRD on Glyph of Warding (emphasis mine):

Spell Glyph: You can store any harmful spell of 3rd level or lower that you know. All level-dependent features of the spell are based on your caster level at the time of casting the glyph. If the spell has a target, it targets the intruder. If the spell has an area or an amorphous effect, the area or effect is centered on the intruder. If the spell summons creatures, they appear as close as possible to the intruder and attack. Saving throws and spell resistance operate as normal, except that the DC is based on the level of the spell stored in the glyph.

When I cast the spell version of Glyph of Warding, do I have to expend an additional spell per day or spell slot to store the spell within it (effectively casting the spell into the glyph), or does the spell/slot expended to cast the Glyph cover that cost?

Please note the rules-as-written tag. Answers should be based on a strict interpretation of the actual rules text, not house rules or DM judgement calls.

Answer 1

The spell description specifies a spell you know and not a spell you could cast and doesn't specify that an additional spell slot is consumed. This may be a bit circuitous, but since there is no evidence that you would need to expend an additional spell slot, I think the logical conclusion is that only one spell slot is needed.

Answer 2

RAW: you “store” the spell; you do not “cast” it. Casting the Glyph only uses the spell slot for the Glyph.