Separate holdings or shared vault space.
Commingled storage pools equivalent products with other investors' holdings. The depository records your type and quantity, and withdrawals are fulfilled with equivalent metal.
Segregated storage keeps your specific pieces physically separate. That can provide clearer item identification and a simpler audit story, but it usually costs more.
Both methods can be compliant for IRA metals when the depository and custodian meet IRS requirements. The best fit depends on product type, holding size, cost sensitivity, and whether receiving the exact original pieces matters.