Why I can start Two instances with the same ORACLE_SID?
oracle 11622 1 0 02:33 ? 00:00:08 ora_pmon_XNORA11
oracle 11624 1 0 02:33 ? 00:00:08 ora_psp0_XNORA11
oracle 11627 1 1 02:33 ? 00:10:21 ora_vktm_XNORA11
oracle 11631 1 0 02:33 ? 00:00:01 ora_gen0_XNORA11
oracle 11633 1 0 02:33 ? 00:00:03 ora_diag_XNORA11
oracle 11635 1 0 02:33 ? 00:00:05 ora_dbrm_XNORA11
oracle 11637 1 0 02:33 ? 00:02:00 ora_dia0_XNORA11
oracle 11639 1 0 02:33 ? 00:00:03 ora_mman_XNORA11
oracle 11641 1 0 02:33 ? 00:00:46 ora_dbw0_XNORA11
oracle 11643 1 0 02:33 ? 00:01:17 ora_lgwr_XNORA11
oracle 11645 1 0 02:33 ? 00:00:19 ora_ckpt_XNORA11
oracle 11647 1 0 02:33 ? 00:00:06 ora_smon_XNORA11
oracle 11649 1 0 02:33 ? 00:00:00 ora_reco_XNORA11
oracle 11651 1 0 02:33 ? 00:00:12 ora_mmon_XNORA11
oracle 11653 1 0 02:33 ? 00:01:01 ora_mmnl_XNORA11
oracle 11655 1 0 02:33 ? 00:00:00 ora_d000_XNORA11
oracle 11657 1 0 02:33 ? 00:00:00 ora_s000_XNORA11
oracle 11712 1 0 02:34 ? 00:00:00 ora_qmnc_XNORA11
oracle 11726 1 0 02:34 ? 00:00:08 ora_cjq0_XNORA11
oracle 11746 1 0 02:34 ? 00:00:01 ora_q000_XNORA11
oracle 11748 1 0 02:34 ? 00:00:00 ora_q001_XNORA11
oracle 11774 1 0 02:34 ? 00:00:12 /files/oracle_db/u01/app/oracle/product/11.2.0.4/dbhome_1/bin/tnslsnr LISTENER -inherit
oracle 12405 1 0 02:40 ? 00:00:01 ora_smco_XNORA11