DLT & fbackup parameters

[Phil Corchary]

(Thanks everyone for your assistence yesterday).

When using fbackup with a config script, there are params like blocksperrecord and checkpointfreq. The IRCD KB alludes to tuning these for different backup types (e.g. 9 track tape, DDS, DLT, etc.).

Does anyone have any best-practice info about these prams with DTL7000 on K570 with 11.0

TIA.

[James R. Ferguson]

Phil:

The best way to tune this is to try adjusting a few of the parameters yourself.
Here are three documents I found that provide good insight into where to begin.

Document JS09291430 "How to tune the performance of fbackup".

Document PU9408251055 "How to optimize performance of fbackup with a compression DDS drive"

Document KBRC00000196 "Understanding Fbackup/Frecover and Optimizing Backup Performance"

I don't have any magic values for you to use. I like blocksperrecord=64 or 128 with a checkpointfreq=128 or 256 accordingly. The 'blocksperrecord' parameter has generally been shown to have the biggest impact with the 'checkpointfreq' also being rather important. I'd rather gain speed during backup and sacrifice it during recovery, so I don't worry too much about the parameters like 'filesperfsm'. Three to five retries for busy files is more than enough.

...JRF...

[Tim Malnati]

You didn't mention the amount of reader processes you have configured (default is 2). I have found that increasing the readers to 6 or 8 will definitely improve small file performance, particularly with a DLT.

[Phil Corchary]

Thanks for the Info. I've read those articles -- I was looking for info/experience with DLT7000.

I tried as follows:
blocksperrecord 128
checkpointfreq 128
readerprocesses 6
maxretries 4

And the cold backup went from 4.5hrs to 2.75hrs. Should I try blocksperrecord=256?

hsgccu08 # du -ks
137023952 .

Am I getting good density on this DLT? - how do I control compression on the DLT from fbackup?

TIA

[James R. Ferguson]

Phil:

Sure, try <256> for blocksperrecord. Blocksperrecord has the biggest impact on performance.

Document A4303862 notes that the /dev/rmt/Xm files normally give the best compression the device supports.

...JRF...