The best way to resize logfiles is by creating new logfile groups in the new size, then dropping the old logfile groups. Example:
SYS> select * from v$logfile;
GROUP# STATUS
---------- -------
MEMBER
--------------------------------------------------------------------------------
1
D:\DATABASE\TRN3\LOGTRN3_1A.LGF
1
F:\DATABASE\TRN3\LOGTRN3_1A.LGF
2
D:\DATABASE\TRN3\LOGTRN3_2A.LGF
2
F:\DATABASE\TRN3\LOGTRN3_2A.LGF
3
D:\DATABASE\TRN3\LOGTRN3_3A.LGF
3
F:\DATABASE\TRN3\LOGTRN3_3A.LGF
6 rows selected.
SYS> alter database add logfile group 4
2 ('d:\database\trn3\logtrn3_4a.lgf','f:\database\trn3\logtrn3_4b.lgf')
3* size 10240K
SYS> /
Database altered.
SYS> alter database add logfile group 5
2 ('d:\database\trn3\logtrn3_5a.lgf','f:\database\trn3\logtrn3_5b.lgf')
3* size 10240K
SYS> /
Database altered.
SYS> alter database add logfile group 6
2 ('d:\database\trn3\logtrn3_6a.lgf','f:\database\trn3\logtrn3_6b.lgf')
3* size 10240K
SAN.SYS> /
Database altered.
SYS> select group#, status from v$log;
GROUP# STATUS
---------- ----------------
1 CURRENT
2 INACTIVE
3 INACTIVE
4 UNUSED
5 UNUSED
6 UNUSED
6 rows selected.
SYS> alter database drop logfile group 2;
Database altered.
SYS> alter database drop logfile group 3;
Database altered.
SYS> alter system switch logfile;
System altered.
SYS> select group#, status from v$log;
GROUP# STATUS
---------- ----------------
1 ACTIVE
4 CURRENT
5 UNUSED
6 UNUSED
SYS> alter system switch logfile;
System altered.
SYS> select group#, status from v$log;
GROUP# STATUS
---------- ----------------
1 INACTIVE
4 ACTIVE
5 CURRENT
6 UNUSED
SYS> alter database drop logfile group 1;
Database altered.
SYS> select group#, status from v$log;
GROUP# STATUS
---------- ----------------
4 INACTIVE
5 CURRENT
6 UNUSED