Subject: Re: [Bacula-users] Speed of backups

> to get the maximum speed with your LTO-5 drive you should enable data
> spooling and change the "Maximum File Size" parameter. The spool disk
> must be a fast one, especially if you want to run concurrent jobs.
> Forget hdparm as benchmark, use bonnie++, tiobench, iozone.
> Then after after you have enabled spooling, restarted the SD, start
> the backup. Look at the log file for "Despooling elapsed time". This
> will show you how fast the spool file can be written to tape.
> The backup time will increase overall because the data will first be
> written to disk and then to tape, but at least you eliminate the
> network and the data source (server) as bottleneck.
> With spooling enabled and LTO-4 drives I get up 100 - 140 MB/s.
> Ralf

Hi, thanks for your help.

I think I was confusing some terms. The speed I reported was the total
elapsed time that my backup took. But now according to your comments I
got this from my logs:

With spooling enabled:

- Job write elapsed time: 102 MB/s average
- Despooling elapsed time: 84 MB/s average

Without spooling enabled:

- Job write elapsed time: 68 MB/s average

These are averages obtained from a group of 5 or more jobs of each
case (with and without spooling). So I can see that with spooling
enabled the process of writing to tape get higher speeds than
copy-from-fd/write-to-tape without spooling enabled.

Now the question is, why am I getting so low despooling speeds if I
use LTO-5 tapes? Shouldn't I have higher speeds than you with LTO-4

I think the write speed of my tape it isn't the best. Some of my tests
(all with spooling enabled) were done with "Buffer & Block size&...

settings at my storage daemon, but other tests were done without those
settings, so I didn't see any appreciable enhancement of performance
changing the value of block sizes.

What can I do?

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