Slow Duplication to Tape in Netbackup 6.5.2

[Ryan_Greeley]

I can't get more than 30 MB/s when duplicating from disk to tape.  I've tried duplicating from different DSU's on SAN, NAS, and local storage.  None will yield greater than 30 MB/s.

However, I can back up data on the same SAN, NAS, and local storage through the same media server to the same tape drive at 70 - 80 MB/s.  That tells me that the source disk and the tape drive aren't my bottleneck.

I don't understand why a backup can be fast but a duplication with the same source and target can be so slow. 

I've had a case open with support for months and they haven't been much help.  I'm hoping someone here can help me.

Thanks for your time.

[Trevor_Jackson1]

 So this is what I believe happens:

Client to DSSU
1) Data is backed up in smaller chunks and then metadata is collected to build and image file on DSSU
2) the image files and metadata are created in special Symantec tar-ball format.

DSSU to tape using Vault
1) The vault profile checks the DSSU for images which meet the criteria of the profile.
2) Then it reads each metadata file, obtaining a list of image files
3) It then creates its own metadata to create a list of sizable chunks to split the data into buffers (using SIZE_DATA_BUFFERS & NUMBER_DATA_BUFFERS)
4) Then the backup processes pass the information to the buffers, if they are full it waits (there is no shoe-shining on LTO4 drives) the buffer amounts have to be less than or equal to the amount of buffer space each drive has.
5) if Multiplexing is used then there are too many little chunks, the buffers of the drives fill up and do not empty fast enough for the media server buffers to send the next batch, hence why the delay looks like shoe-shining.
6) now if you configure the buffers correctly for the tape drives, in most cases the disk backups will slow down, as they have more and better buffers. So my advice here is to leave everything as is for your first tests.

sdw303's advice on the testing side of things is completely true, the slightest mistake and you have to remove all settings and start again. So play gently people.

If anyone needs more info, let me know.

Trevor