Differential backup files are almost the same size as full backups.

Question

Hello All,
I have done a little research on this topic and feel like we are not doing anything to cause this issue. Any assistance is greatly appreciated. 
The details: Microsoft SQL Server 2008 R2 (SP2) - 10.50.4297.0 (X64)   Nov 22 2013 17:24:14   Copyright (c) Microsoft Corporation  Web Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1) (Hypervisor).  The
database I am working with it 23GB. The full backup files are 23GB, differentials are 16GB (and growing) and transaction logs bounce between 700KB to 20MB. The backup schedules with T-SQL follow:
T-Log: daily every four hours
BACKUP LOG [my_dabase] TO  DISK = N'F:\Backup\TLog\my_dabase_backup_2015_03_23_163444_2725556.trn' WITH NOFORMAT, NOINIT,  NAME = N'my_dabase_backup_2015_03_23_163444_2725556', SKIP, REWIND, NOUNLOAD,  STATS = 10
GO
Diff: once daily
BACKUP DATABASE [my_database] TO  DISK = N'F:\Backup\Diff\my_database_backup_2015_03_23_163657_1825556.dif' WITH  DIFFERENTIAL , NOFORMAT, NOINIT,  NAME = N'my_database_backup_2015_03_23_163657_1825556', SKIP, REWIND, NOUNLOAD,  STATS =
10
GO
declare @backupSetId as int
select @backupSetId = position from msdb..backupset where database_name=N'my_database' and backup_set_id=(select max(backup_set_id) from msdb..backupset where database_name=N'my_database' )
if @backupSetId is null begin raiserror(N'Verify failed. Backup information for database ''my_database'' not found.', 16, 1) end
RESTORE VERIFYONLY FROM  DISK = N'F:\Backup\Diff\my_database_backup_2015_03_23_163657_1825556.dif' WITH  FILE = @backupSetId,  NOUNLOAD,  NOREWIND
GO
Full: once weekly
BACKUP DATABASE [my_database] TO  DISK = N'F:\Backup\Full\my_database_backup_2015_03_23_164248_7765556.bak' WITH NOFORMAT, NOINIT,  NAME = N'my_database_backup_2015_03_23_164248_7765556', SKIP, REWIND, NOUNLOAD,  STATS = 10
GO
declare @backupSetId as int
select @backupSetId = position from msdb..backupset where database_name=N'my_database' and backup_set_id=(select max(backup_set_id) from msdb..backupset where database_name=N'my_database' )
if @backupSetId is null begin raiserror(N'Verify failed. Backup information for database ''my_database'' not found.', 16, 1) end
RESTORE VERIFYONLY FROM  DISK = N'F:\Backup\Full\my_database_backup_2015_03_23_164248_7765556.bak' WITH  FILE = @backupSetId,  NOUNLOAD,  NOREWIND
GO
As you can probably tell we are not doing anything special in the backups, they are simply built out in MSSQL Management Studio. All databases are set to full recovery mode. We do not rebuild indexes but do reorganize indexes once weekly and also update
statistics weekly.
Reorganize Indexes T-SQL (there are 255 indexes on this database)
USE [my_database]
GO
ALTER INDEX [IDX_index_name_0] ON [dbo].[table_name] REORGANIZE WITH ( LOB_COMPACTION = ON )
GO
Update Statistics T-SQL (there are 80 tables updated)
use [my_database]
GO
UPDATE STATISTICS [dbo].[table_name]
WITH FULLSCAN
GO
In a different post I saw a request to run the following query:
use msdb
go
select top 10 bf.physical_device_name, bs.database_creation_date,bs.type
from  dbo.backupset bs
inner join dbo.backupmediafamily bf on bf.media_set_id=bs.media_set_id
where   bs.database_name='my_database'
order by bs.database_creation_date
Results of query:
physical_device_name database_creation_date type
F:\Backup\Full\my_database_backup_2015_03_07_000006_2780149.bak 2014-02-08 21:14:36.000 D
F:\Backup\Diff\Pre_Upgrade_OE.dif 2014-02-08 21:14:36.000 I
F:\Backup\Diff\my_database_backup_2015_03_11_160430_7481022.dif 2015-03-07 02:58:26.000 I
F:\Backup\Full\my_database_backup_2015_03_11_160923_9651022.bak 2015-03-07 02:58:26.000 D
F:\Backup\Diff\my_database_backup_2015_03_11_162343_7071022.dif 2015-03-07 02:58:26.000 I
F:\Backup\TLog\my_database_backup_2015_03_11_162707_4781022.trn 2015-03-07 02:58:26.000 L
F:\Backup\TLog\my_database_backup_2015_03_11_164411_5825904.trn 2015-03-07 02:58:26.000 L
F:\Backup\TLog\my_database_backup_2015_03_11_200004_1011022.trn 2015-03-07 02:58:26.000 L
F:\Backup\TLog\my_database_backup_2015_03_12_000005_4201022.trn 2015-03-07 02:58:26.000 L
F:\Backup\Diff\my_database_backup_2015_03_12_000005_4441022.dif 2015-03-07 02:58:26.000 I
Is your field ready?

Answer 1

INIT basically intializes the backup file, in other words, it will overwrite the contents of the existing backup file with the new backup information. 
basically, what  you have now is you are appending all you backup files  (differentials) one after the other (like chain).
you do not necessarily have to do it.  these differential backups can exist as different files.
Infact, I would prefer them to separate, as it gives quick insight on the file, instead doing a  "restore filelist" command to read the contents of the backup file.
The point Shanky, was mentioning is that : he wants to make sure that you are not getting confused between the actual differential backup file size to the physicial file size(since you are appending the backups) example : if you differential backup is 2
gb, and over the next five you take a differential backup and append to a single file,like you are doing now,  the differential backup file size is 2gb but you physicial file size is 10Gb.  he is trying to make sure you are confused between these
two.
Anyways, did you get a chance to run the below query and also did you refer to the link I posted above. It talks a case when differential backups can be bigger than full backups and ' inex reorganize' or 'dbcc shrinks' can cause this. 
--backup size in GB
select database_name,backup_size/1024/1024/1024,Case WHEN type='D' then 'FULL'
WHEN type='L' then 'Log'
When type='I' then 'Differential' End as [BackupType],backup_start_date,backup_finish_date, datediff(minute,backup_start_date,backup_finish_date) as [BackupTime]
from msdb.dbo.backupset where database_name='mydatabase' and type in ('D','I')
order by backup_set_id desc
Hope it Helps!!