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Kern Sibbald wrote:
> Hello,
>
> On Tuesday 29 July 2008 15:22:03 T. Horsnell wrote:
>> What:
>> That Bacula be modified to enable the simultaneous use of multiple tape
>> drives, either as a bunch of freestanding units or as multiple drives in
>> an autochanger.
>>
>> Why:
>> For me personally, this would permit faster simpler backup of a large
>> single filesystem. I have a two-drive LTO4 tapechanger and at present,
>> in order to utilise both drives at once, I have to create two jobs each
>> of which backs up part of the filesystem. This is not optimal as the two
>> subparts can change size radically, meaning that one drive may spend
>> much of its time idle. I also have to split my tapes into two pools, one
>> for each job.
>> I have seen one other similar request to the users list recently,
>> whereby a user had a bynch of freestanding drives which he wanted to
>> preload with a set of tapes once a week, and then have Bacula
>> automatically organise his backup over the tapes as it saw fit.
>> This may make a cheap alternative to a tapechanger.
>>
>> A device pool maybe?
>
> Technically I don't know how to do this project. The SD has blocks of data
> coming in from the FD, and sending those blocks to multiple drives would be
> extremely difficult to track -- I am not even sure how. Currently, they are
> either sequential (if spooling is on) or at least written in order to a
> single drive, so it is very easy to track and find them for restores.
>
> In addition, I don't think it is possible for any existing network connection
> to run fast enough to drive an LTO4 tape drive at full speed, so this project
> seems to add a lot of complexity to Bacula to give no improvement in
> performance. If I am wrong about the network connection and an LTO4, please
> show me the math :-)
>
> For the moment I cannot accept the Feature Request. If you can give complete
> details of a design for tracking the blocks written to multiple tapes and how
> to send them back to the FD in the same order, and if you can show with a
> simulation that we would actually gain something, then you can resubmit it,
> and I will reconsider adding it to the projects. After than, either someone
> must submit a patch or the Bacula users vote and it becomes a top rated
> project, in which case one of the developers would surely work on it.
>
> Best regards,
>
> Kern
>
> PS: Normally, I don't veto a Feature Request even if I am not much in favor
> of
> it unless it involves license problems (using proprietary interfaces) or is
> technically not possible as is the current request as written.
- From what I've seen in HP's Data Protector, the way that it determines
how to split jobs over different tape drives is to go by filesystem. It
calls each filesystem an object and at the start, it decides what drive
it will go to. Not sure if that helps any, but... there it is.
- --
---- _ _ _ _ ___ _ _ _
|Y#| | | |\/| | \ |\ | | |Ryan Novosielski - Systems Programmer II
|$&| |__| | | |__/ | \| _| |novosirj AT umdnj DOT edu - 973/972.0922 (2-0922)
\__/ Univ. of Med. and Dent.|IST/AST - NJMS Medical Science Bldg - C630
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