Re: [Bacula-users] how to debug a job

Hello,

2015-01-23 21:42 GMT+01:00 Dimitri Maziuk <dmaziuk AT bmrb.wisc DOT edu>:

On 01/23/2015 02:33 PM, Radosław Korzeniewski wrote:

> No, it is not working as you described.
> Data spooling will read stream from the client, then write it to the
> temporary disk file, then during despool it is stopping a stream from the
> client, reads a temporary file and write to destination volume.
> A standard job will never stop reading a stream and direct write data to
> the volume.

Read the last bulletpoint under "Other considerations" in
http://www.bacula.org/5.2.x-manuals/en/main/main/Data_Spooling.html#SECTION003130000000000000000

Then read "10 clients" again.

Yes, I've read. When you do a backup without spooling you can issue any number of jobs writing to the disk storage as you wish. All of them will be writing backup stream as fast as it can get it from the client. No any additional processing is involved. For disk storage it is a fastest way of doing backups with Bacula. Tested. Sure, you should enable attribute spooling.

With data spooling you are coping the same data from place to place which takes time and slow down a backup. Additionally when Bacula despooling the job stop getting data from a client. Let's count:

- client can supply a backup stream 100MB/s over a 1Gbit/s Ethernet

- server can write or read 100MB/s on the storage

- backup size 6GB (6000MB for rounding in our calculation)

- spooling 10GB - it can spool/despool in one loop

Without spooling we can finish a backup in 60 seconds - 1 minute

With spooling we write 6GB os backup stream to the disk spool area which take 1 minute, next we need to read spooled data from spooling area and write it to the main storage which takes another 60 seconds. Overall backup time is 2 minutes.

Summary:

1 minute for backup job without spooling, backup speed = 100MB/s

2 minutes for backups with spooling, backup speed = 50MB/s

Spooling data for disk based backups will slow down every backup 2 times, which was to prove.

Do you have a problem with multiple jobs write to the disk storage? I never had this kind of problem in any of my dozen of deployments.

What you should read from the page you provided:

" (...) It probably does not make a lot of sense to enable data spooling if you are writing to disk files. (...) "

You should gain 2x speedup in your all backups when you disable data spooling.

best regards

Radosław Korzeniewski
radoslaw AT korzeniewski DOT net

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