DSSU - Staging & Watermarks

[SYMAJ]

After much investigation, reading and research I still have a confusion over the operation of a basic disk DSSU and it's staging to tape.  Let me give an example:

Storage Unit created on local disk, specified as BASIC disk, on demand only, low watermark 20%, high watermark 80%, staging schedule set to run 24x7 - hourly to tape.

In this instance my understanding is as follows:

1. data is written to the DSSU during the backup window

2. every hour the staging shcedule runs and will duplicate ALL images not already duplicated to the tape storage unit

3. during the backup window should the storage unit not have sufficient space for a backup image then the oldest (assuming no data classification) image which has already been copied to tape will be deleted from disk and the new backup image will be written to the DSSU.

4. should there be no images when the DSSU staging schedule runs every hour then the staging job simply starts and finishes with no action

Where do the watermarks come in ?  I have read various explanations - and in the case of BASIC disk some say the watermark values are not considered, some say that the low watermark is ignored, some say the high watermark is ignored.......  My confusion lies in the area of when the images on disk are deleted, and how many are deleted.  i.e. if the watermarks are valid, then when the DSSU reaches the high watermark (assuming all images have been copied to tape already) do sufficient images get deleted to bring the capacity down to the low watermark ?  Obviously I wamt to keep as many images on disk as possible, so should I have the high watermark at the default 98%.  If the watermarks are ignored then I believe that all images will remain on disk until a status 129 (disk full) occurs, then a backup will pause, images will be deleted (but how many ??) and then the backup will re-commence.

Confused.......

AJ.

[Nicolai]

It's quite a while since I used the DSSU - today I use advanced disk with SLP's. But I did find some T/N explaining DDSU cleaning behavior. Hope thy clear the misunderstanding.

http://www.symantec.com/docs/TECH44719

http://www.symantec.com/docs/TECH66149

[Marianne]

The above 2 TN's should clear all confusion!!

[SYMAJ]

OK - I had seen the first but not the second.  I too am using either 5220 appliances or Advanced disk nearly all the time, not been near DSSU for a good while.

The second technote helps, but just to check I understand this correclty is the following then true (forget the staging to tape as I will run this every hour as per above so assume all images are on tape):

Say High water mark is 90% and low water mark is 20%.

The disk will keep filling up until 90% is reached.

The cleanup will come in and expire sufficient images to attain the 20% full capacity

During the cleanup backups will continue

If my understanding above is correct, then surely I want to keep the low watermark as high as possible to ensure that i keep the images on disk for as long as possible ?  I understand that if I have say 90% high and 80% low then the cleanup will be called far more frequently but will have less to do.  If I recall correctly 98% and 85% are the defaults - are these generally good values with a relatively small capacity DSSU (5TB) ?

Is my take on this correct or am I missing something (and still confused....) ?

AJ

[mph999 · Accepted solution]

You are correct:

Say High water mark is 90% and low water mark is 20%.

The disk will keep filling up until 90% is reached.

The cleanup will come in and expire sufficient images to attain the 20% full capacity

During the cleanup backups will continue

*********************

Just a note.

It will only delete images that have been duplicated, and will 'try' to get down to 20% if possible.

I think running jobs continue, but it doesn't start new until it has cleaned up space, but I'm not 100% sure on this without testing it.

Martin

[Marianne]

If I recall correctly 98% and 85% are the defaults - are these generally good values with a relatively small capacity DSSU (5TB) ?

There is unfortunately no easy answer and you will have to find values that work for you.

All depends on the size of backups that you take on a daily basis. Lots of small images will be fine with higher low water mark. Mostly large backup images may battle with low water mark of 85%.

My recommendation will be to start with defaults, monitor disk usage and cleanup closely. Ensure you have bpdm and admin logs enabled for this. Adjust as you see fit.

[Nicolai]

Just a FYI

If the DSSU is filling to quickly to may have to lower the high watermark. I have had a couple of incident in the DSSU glory time where the DSSU was filling quickly than Netbackup was able to delete staged backups.

[SYMAJ]

OK - thanks to everyone for the input - my confusion has now been clarified !!

AJ

[Nicolai]

Glad to hear 

Please mark the post that best answered the question as a solution.

[SYMAJ]

I had already marked this item as SOLVED, but I see now it is not showing as such.  I do not now have the option for marking an entry as SOLVED, it appears that this poarticular post is 'in limbo'.

Moderator / administrator help ??

AJ

[Mark_Solutions]

It has happened to a few threads today - i will add this to the list!