Hi,
16.02.2010 21:37, Edward M. Markowski wrote:
>
> I thought about this reciently, after I moved my spool dir to a 1.5 GB
> ramdisk, I had been using 100GB of a mirrored pair of 500GB SATA drives
> my throughtput to tape went up be a little over 10Mps.
>
> A few thoughts, see inline......
>
> On Tue, 16 Feb 2010, Arno Lehmann wrote:
>
>> Hi,
>>
>> 16.02.2010 11:50, Daniel Kamm wrote:
>>> That's maybe a stupid question, but I really wonder...
>>>
>>> Using Disk Spooling prior to write data to tape, heads in a sequential
>>> write order:
>>> a) write data from backup client to disk spool directory
>>> b) write data from spool directory to tape
>>>
>>> Why are those tasks done sequentially?
>>
>> I know those three reasons:
>> - simultaneously spooling and despooling increases the requirements of
>> your spool space storage system even more
>
> agree, but space is cheep, even boatloads of RAM :-)
With RAM disk, you indeed get a fast file system. However, many users
of Bacula will not be able to add (or willing to pay for) RAM to get a
useful spool ramdisk.
Thus the approach to use must work reasonably fast with hard disks -
size is not so much the problem here, rather the IO load. And, when
using a small number of disks, this is typically the bottle neck.
>
>> - it's never been implemented
>> - it's probably harder to implement than it looks at first.
>
> One way to implements this is to have several smallish spool partitions
> with the producer and consumer processes never using the same one at the
> same time. For this to be most efficient the partitions would have to
> be on different disks/busses/controllers.
>
> A better way in my opinion is to used a spool sized ring buffer in
> memory rather then a disk based spool. The consumer would only start
> after the producer had put a large set amount in it and continued until
> drained the buffer.
Sure... those approaches are not exactly new, and they don't sound too
complicated. However, to discuss this, -users is not the best place.
If you want to propose an implementation, you should do that on -devel
- I'm sure Kern would like to see actual patches ;-)
My understanding of the situation is that, once you want to actually
implement simultaneous spooling and despooling in a way that
integrates well with Bacula you find there's a lot more work to be
done than you expect at the beginning...
Cheers,
Arno
>
>>
>>> Let's say if the spool is reaching a waterlevel mark, the storage daemon
>>> will start to write the spool data to tape _and_ at the same time the
>>> backup client still sends data to the spool directory. Isn't that
>>> possible?
>>
>> It's not possible now, but IIRC this has been discussed quite often,
>> but, while many users thought it might be a nice feature, nobody
>> started actually working on it.
>>
>> There's actually a feature request regarding that, though it isn't on
>> the web site yet. It is, though still unnumbered, in the projects file
>> of the git tree.
>>
>> Cheers,
>>
>> Arno
>>
>>> Cheerz,
>>> - Dan
>>>
>>> ------------------------------------------------------------------------------
>>>
>>>
>>> SOLARIS 10 is the OS for Data Centers - provides features such as
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>>
>> --
>> Arno Lehmann
>> IT-Service Lehmann
>> Sandstr. 6, 49080 Osnabrück
>> www.its-lehmann.de
>>
>> ------------------------------------------------------------------------------
>>
>>
>> SOLARIS 10 is the OS for Data Centers - provides features such as DTrace,
>> Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW
>> http://p.sf.net/sfu/solaris-dev2dev
>> _______________________________________________
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>>
>>
>>
>>
>>
>
> !DSPAM:4b7b01f411881014520154!
--
Arno Lehmann
IT-Service Lehmann
Sandstr. 6, 49080 Osnabrück
www.its-lehmann.de
------------------------------------------------------------------------------
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