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Re: [Bacula-devel] concurrent multidrive use


OK, thanks. And sorry to have pestered the development *and* the users 
list about this. I just wanted to be sure you understood what I meant.

Actually, I would have said that striping was the process of spreading a 
single *file* across multiple drives simultaneously (just like 
disk-striping). To my mind, spreading the files of a single *job* across 
multiple drives doesnt mean that part of each *file* is written to 
multiple drives, but instead, that when the storage daemon is writing to 
a device which has been declared as an autochanger with multiple drives, 
it would take the next file from its input stream and write it to an 
idle drive in that autochanger.

I guess if the storage-daemon scheme has one thread per tapedrive,
it doesnt lend itself to this mode of operation.

THanks again,
Terry

Kern Sibbald wrote:
> Yes, sorry, I did not understand.  Bacula does not have the ability to write a 
> single job to multiple drives -- normally that is called striping.  It is 
> unlikely that it will be implemented any time in the near future.
> 
> 
> 
> On Monday 21 July 2008 18:27:43 T. Horsnell wrote:
> 
>>Thank you for that quick reply, and once again, apologies for the
>>interruption, but I dont want to split the backup across multiple jobs,
>>(with part of the filesystem being handled by one job and part by the
>>other), because however I make the split, the content (and hence the
>>size) of each part of the filesystem will be continually changing (this
>>is a 16TB multiuser raid system), and so one tapedrive may well be
>>mostly idle whilst the other one is continually busy. So I want, if
>>possible, to do this with a single job.
>>
>>Cheers,
>>Terry
>>
>>Kern Sibbald wrote:
>>
>>>Hello,
>>>
>>>We generally do not supply support help on this list, but I will give a
>>>few tips ...
>>>
>>>Bacula has been able to write to multiple drives simultaneously for a
>>>very long time now -- many years and many versions.
>>>
>>>The simplest way to do it is to use different pools for each job.
>>>
>>>A not so satisfactory way of doing it is to use "Prefer Mounted Volumes =
>>>no". I don't recommend this as it leads to many operational problems.
>>>
>>>In general, if you are backing up raid disks, you should be able to tune
>>>your hardware so that it will write approximately 150 MB/sec with Bacula
>>>to an LTO3 drive, and so splitting jobs is not generally necessary. 
>>>Getting your hardware tuned to run at those speeds is not easy and
>>>requires professional help.
>>>
>>>Best regards,
>>>
>>>Kern
>>>
>>>On Monday 21 July 2008 17:20:11 T. Horsnell wrote:
>>>
>>>>Apologies for pestering the developers list, but I cant determine from
>>>>the user docs whether what I want to do is failing because I'm doing it
>>>>wrongly, or simply that its not supported.
>>>>
>>>>I want to define a single job which will backup a single (big) raid
>>>>filesystem to an autochanger which contains multiple tapedrives, and I
>>>>want this job to use all the tapedrives simultaneously. This would seem
>>>>to me to be a pretty standard requirement, but I cant get it to work
>>>>with Bacula version 2.4.1
>>>>
>>>>Looking at the Storage Daemon section (6.4) in the new delvelopers docs
>>>>for 2.5.2 (dated 20th July 2008 !) I see that this may not yet be
>>>>possible:
>>>>
>>>>
>>>>---cut---
>>>>Today three jobs (threads), two physical devices each job writes to only
>>>>one device:
>>>>Job1 -> DCR1 -> DEVICE1
>>>>Job2 -> DCR2 -> DEVICE1
>>>>Job3 -> DCR3 -> DEVICE2
>>>>
>>>>To be implemented three jobs, three physical devices, but job1 is
>>>>writing simultaneously to three devices:
>>>>
>>>>Job1 -> DCR1 -> DEVICE1
>>>>        -> DCR4 -> DEVICE2
>>>>        -> DCR5 -> DEVICE3
>>>>Job2 -> DCR2 -> DEVICE1
>>>>Job3 -> DCR3 -> DEVICE2
>>>>---cut---
>>>>
>>>>Is what I want possible in 2.5.2, or should I wait?
>>>>
>>>>Cheers,
>>>>Terry.
>>>>
>>>>
>>>>
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> 
> 


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