To me it makes sense to separate the logs by day. EXEC sp_cycle_errorlog will create a new SQL Server error log.  I normally create a job that runs a midnight and creates a new error file.  By default, SQL Server only keeps 6 error log files and I normally increase that number to 30.

Files To Keep
If the server has already been set up, I normally use the GUI by right clicking on SQL Server Logs and choose configure. If I am setting up the server, I have this piece of code in my scripts.

[sourcecode language=”sql”]
USE [master]
GO
EXEC xp_instance_regwrite N’HKEY_LOCAL_MACHINE’, N’SoftwareMicrosoftMSSQLServerMSSQLServer’, N’NumErrorLogs’, REG_DWORD, 30
GO
[/sourcecode]

Cycling the Logs
This code will create a new job to run at midnight and cycle the logs.

[sourcecode language=”sql”]

USE [msdb]
GO

/****** Object: Job [Cycle Error Log] Script Date: 08/01/2014 13:31:39 ******/
BEGIN TRANSACTION
DECLARE @ReturnCode INT
SELECT @ReturnCode = 0
/****** Object: JobCategory [[Uncategorized (Local)]]] Script Date: 08/01/2014 13:31:39 ******/
IF NOT EXISTS (SELECT name FROM msdb.dbo.syscategories WHERE name=N'[Uncategorized (Local)]’ AND category_class=1)
BEGIN
EXEC @ReturnCode = msdb.dbo.sp_add_category @class=N’JOB’, @type=N’LOCAL’, @name=N'[Uncategorized (Local)]’
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback

END

DECLARE @jobId BINARY(16)
EXEC @ReturnCode = msdb.dbo.sp_add_job @job_name=N’Cycle Error Log’,
@enabled=1,
@notify_level_eventlog=0,
@notify_level_email=0,
@notify_level_netsend=0,
@notify_level_page=0,
@delete_level=0,
@description=N’No description available.’,
@category_name=N'[Uncategorized (Local)]’,
@owner_login_name=N’sa’, @job_id = @jobId OUTPUT
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
/****** Object: Step [Cycle Error Log] Script Date: 08/01/2014 13:31:40 ******/
EXEC @ReturnCode = msdb.dbo.sp_add_jobstep @job_id=@jobId, @step_name=N’Cycle Error Log’,
@step_id=1,
@cmdexec_success_code=0,
@on_success_action=1,
@on_success_step_id=0,
@on_fail_action=2,
@on_fail_step_id=0,
@retry_attempts=0,
@retry_interval=0,
@os_run_priority=0, @subsystem=N’TSQL’,
@command=N’EXEC sp_cycle_errorlog’,
@database_name=N’master’,
@flags=0
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_update_job @job_id = @jobId, @start_step_id = 1
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobschedule @job_id=@jobId, @name=N’Midnight Ride’,
@enabled=1,
@freq_type=4,
@freq_interval=1,
@freq_subday_type=1,
@freq_subday_interval=0,
@freq_relative_interval=0,
@freq_recurrence_factor=0,
@active_start_date=20140801,
@active_end_date=99991231,
@active_start_time=0,
@active_end_time=235959
— @schedule_uid=N’bca9d15e-e47f-40a4-a236-e14020f77b76′
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobserver @job_id = @jobId, @server_name = N'(local)’
IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback
COMMIT TRANSACTION
GOTO EndSave
QuitWithRollback:
IF (@@TRANCOUNT > 0) ROLLBACK TRANSACTION
EndSave:

GO

[/sourcecode]