Using a DLT Tape with fbackup

[Darren Brown]

What are the best settings for the fbackup_config file to get the best performance out of the DLT

[Stefan Farrelly]

After a lot of testing we found the following fbackup options the best;

blocksperrecord 128
records 32
checkpointfreq 256
readerprocesses 4
maxretries 1
retrylimit 0
maxvoluses 500

[George LaSalle]

One thing to keep in mind about DLTs is that they do not seem to do a very fast search, at least with fbackup. For example, our backup takes about 8hrs and to locate a file at the end of the tape takes 2hrs. This is despite the fact that HP says they have an average of 45sec seek time on a DLT 40 with 40GB of data and they say they have "Tested compatibility with all major servers, software and operating systems"(see http://www.hp.com/tape/datasheets/dlt40.html#specs) .
I have a call open with the RC on this. As I understand it, DAT drives(which do have a very fast search with fbackup/frecover) put Fast Search Marks where ever they want, based on the fbackup filesperfsm parameter. DLTs must put the FSMs between files along with the file markers. We have a mix of a lot of small files and some big(200-500mg) database files. I have not found a filesperfsm setting that gets searches down under this 2hr figure and does not slow the backups down.

[Darren Brown]

I tried the swettings suggested by Stefan and got the following result:

It took 2736 seconds to back up 2134094 blocks

This is not even as good as DDS.

[Stefan Farrelly]

Hmm. What speed is your DLT drive ?
Is your DLT drive on a SCSI bus on its own ? (ie. not sharing with any disks).

The older DLT drives (2000/3000/4000) arent any quicker than a good DDS2/DDS3 drive anyway. If you tell me what model your DLT drive is I will tell you whats the maximum speed you will get out of it with dd/fbackup.

[Darren Brown]

ioscan says QUANTUM DLT8000. The manual calls it A1375A and says that the sustained transfer rate is 6MB/s ( 12MB with compression ). It does that if I use dd with bs=256k; I copied 1164MB to tape in 204 seconds.

What I need now is to get fbackup to do likewise

[Stefan Farrelly]

I just noticed on one of our systems we dont use an fbackup config file at all, we use the defaults, and we backup 18.7GB/Hr = 5.2 MB/s to our DLT8000 - which is on a bus of its own. Ive searched around, cant find any mention anywhere of optimal fbackup settings for a DLT drive, sorry. Have to be trial and error and figure it out yourself. Just try upping the blocksize slowly, that should eventually show the optimal setting (blocksperrecord and records).