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Files not overwriting

Created: 19 Feb 2013 • Updated: 21 Mar 2013 | 11 comments
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Once again, let me say that I am new to Backup Exec. I have all of our servers backing up to 2 different storage devices.  I believe I have the backup jobs set up identical to each device, however I am seeing one main difference between the files on the devices. The one device never gets full, it always maintains about the same amount of free space.  The second device always gets full, I have to go in and manually delete the files so I do not receive failed jobs.  My first thought is that I did not have the media sets set up correctly, so I created a new media set.  I specified that I wanted the data to append and overwrite in 45 days.  However with that said and done I still have files from more than 45 days ago.  I want this device to be self sustaining like the other device.

The second thing that I need is some advice...  What is the ideal size for back up files?  I have just taken over the back up's for the company I work for and they had the file size limit set from any from 1 GB to 999GB.  I always thought 4 GB was a good limit, although I am guessing that it should also be dependent on the amount of data in which you are backing up.

I would appreciate some input on these 2 questions.  Thanks for your time.

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Gurvinder Rait's picture

There are 2 parameters to media set. Append and overwrite protection period. This is important to know that overwrite protection period is counted from the date the append period ends

for example if APP - 2 days, then the b2d or tape will be appendable for 2 days. In this time period if the B2D has space then the data can be appended to it. When this append perios ends then starts the overwrite protection period. So for example if the OPP is set to 2 days , that means the bkf or tape will be protected for 2 days after the append period ended.

Please refer this link as well : 

For the second part of the question I would recommend the bkf file size be around the size of the backup. The positives are that Backup Exec has to then mount the media less times and it can carry on writing to it. Secondly, select the maximum size when  creating the backup-to-disk file, this will help reduce fragmentation. Refer Admin Guide for Backup Exec 2010 and look under the following topic Creating a backup-to-disk folder by setting properties (download admin guide from

CraigV's picture

So if a backup job is 500GB would you recommend creating a B2D file size of 500GB?

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Gurvinder Rait's picture

Craig, I would like to correct myself. Would not really want the size of the bkf to be that large since as you pointed out there are chances a slight corruption could cause major damage and entire set might not be recoverable.

On the contrary if the disk is fast and end user is duplicating the data as well, in that case I think it should be ok. Depends really how much of a performance gain is achieved with setting the size large, allocate the entire space along with the read/write settings of the B2D. Would you agree to this ? 

CraigV's picture

No I wouldn't to be honest. The performance you gain by streaming 1 x 500GB flat-file to tape is offset by the chance of losing 100% of your backups, no restores, lots of trouble. The speed of disk plays no role here. I could run backups to EFD disks and still lose everything in 1 file.

Nowhere does it mention in any Symantec article that having 1 file is recommended, and the forums are rife with advice against it.


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CraigV's picture


Never append to B2D should always overwrite them. It is a recommendation from Symantec. This is probably why you have files for longer than 45 days in your backups...

On the size of your B2D files...4GB is the minimum, but the larger you go, the more risk you take in losing data if a *.bkf file is corrupted. I've seen anything from the default 4GB to 100GB (I wouldn't recommend this). Maybe increase the size fo 10GB and see what difference it makes.


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prs246191's picture

So is my thinking wrong if I want to allow media to be added to the current media set to 7 days and be kept for 45 days, I would set my append value to 7 and my overwrite protection to 38?  More or less my goal is I want to have backups for 30 to 45 days of our servers, which we have now, but I want the one device to overwrite its' bkf files after the for mentioned length of time

Also why is it not recomended to append B2D files? Why would you not want to allow media to be added to a media set?  If this is the case should I set my append to 0 and overwrite to 45?

Also back to the subject of recomended file size is it correct to assume that if you had 5 files of 10gb each, if one got curropted that you would still be able to get data of the other 4?

As always thanks for the knowledge!

pkh's picture

The OPP starts from the end of the last job that writes to the media and NOT from the end of the AP.  Here is a quote from the document referenced earlier

The Overwrite protection period starts at the end of each job run, not the beginning. It is lengthened each time a media is modified.

As such, each time to append to the media, the protection period for the entire media gets extended.

This is the reason why it is not recommended that you append to disk media is that you only prolong the protection period of the media.  Suppose Job1 writes 30GB of data to a disk media on Monday and the OPP is set to 3 days, so the media is protected until Thursday.  If on the following day (Tuesday), Job2 appends to the media, the media will be protect for 3 days from Tuesday which is Friday.  The 30GB which could have been reused on Friday is now no longer available.  For tape media,  we append to them to maximise the use of the tape capacity.  For disk media, there is no advantage to append to a media because the media is only as large as the data in it.  It is for this reason that in BE 2012, you are not given the option to append to disk storage or disk cartridge devices.

Be careful when you specify allocate max size.  When you have this option, BE will allocate the max size even if it needs to write 1MB.  Suppose you say allocate max size of 100GB and BE needs to write 1MB, it will allocate 100GB.  If there is, say, only 90GB of space left on your disk, your job will fail because BE cannot find 100GB to allocate the .bkf file.  If you don't check the allocate max size checkbox, then BE will allocate and use only the disk space that it needs which in this example is 1MB.

You have to use your judgement as to what the max size should be.  If your backups are huge like 200GB, then leaving it at the default 4GB would mean that you have a lot of small files and will fragment your disk.  Also there are overheads involved when the system allocate a new file.  For this example, I would use something like 40 - 50GB as the max size, so that there are not too many files to be allocated.


To know why one of your disk is full and the other is not.  Check what is being written on the disk and when they expire.   How much you can put on the disk and how long you can retain the data depends on the size of your data and the size of your disk.  Depending on the size of your data, you need to calculate whether it will fit onto your disk if you adopt a certain OPP.  If not, then either get a bigger disk or shorten the OPP.

If your disks are in a device pool, note that BE will write to the first available disk.

prs246191's picture

I now understand why you would not want to allow media to be appendend to a b2d.  However I do have a question about unchecking the "Allocate the maxium size for b2d files".  When you uncheck that box another option becomes availible "Maxium number of backup sets per b2d file.  Am I correct in assuming that this is the total amount of files allowed for one job.  For example, if you were backing up 200gb worth of data and the max size for b2d files was 50gb you would want to set max number of backup sets per b2d file to atleast 4?


Gurvinder Rait's picture
Maximum number of backup sets per backup-to-disk file - 
Lets say you have 2 backup jobs and they are backing up C and D drive respectively. The first creates a C Drive Backup Set and lets say the next backup appends to the same bkf since the maximum size of the bkf file is not reached. If that case you would probably have 2 backup sets in that bkf (if both complete on that same bkf) Similarly you can have more backup sets if there is space available.
Fewer backup sets in a backup-to-disk file mayallow the overwrite protection period to expire sooner, and disk space to be reclaimed faster
Refer :
pkh's picture

Backup sets in this case refers to a resource that is backed up, like the C: drive, D: drive, system state, SQL database, etc.  When you hit the max backup set limit, a new .bkf file would be created.  Suppose you set the max backup set to 10 and you are backing up the C; drive and system state of 10 servers.  After 5 servers (2 backup sets * 5 servers) you would have hit the max backup set limit, even if the max size is not reached, a new .bkf file would be created for the backup of the subsequent servers.  The default limit of 100 should be more than sufficient.

prs246191's picture

I just needed to learn how to configure media sets properly.