Hi,

05.09.2008 03:24, Jose Ildefonso Camargo Tolosa wrote:
> Hi!
> 
> On Fri, Sep 5, 2008 at 4:17 PM, Ryan Novosielski <novosirj AT umdnj DOT edu> 
> wrote:
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>>
>> This is why I said that you'll almost always be shoeshining without
>> spooling. Many modern drives are so fast that you theoretically need to
>> have perfect conditions to avoid shoe-shining. Though, I suppose if
>> you're streaming a LOT of data, you're OK.
>>
>> I wonder how many drives do variable speed writing.

As far as I know, all current-technology drives that can write really 
have that feature. All the LTO drives I read the specs on do, at least.

The range of speeds they can use vary a bit, though.

> I wonder *how* the tape tells that it have to reduce its speed,

When the buffer in the tape drives runs out of data. Essentially the 
drive is capable to measure the speed with which data is fed to it and 
tries to adjust speed accordingly.

> I
> think that bacula should instruct it to reduce its speed as part of
> the configuration (similar as how a cd-r drive modifies its speed
> *before* starting the write process).

No, this is not something you can set from a user program. The vendor 
tools might be able to do so, but the automatic speed adaption is 
reliable enough to simply use it and don't worry about it.

> 
>> John Huttley wrote:
>>> To follow up, LTO drives are very fast and this can be a liability.
>>> However some drives, notably those by HP and some models by Tandberg support
>>> variable speed writing. Normally down to 50% of normal.
>>> These are resistant to shoe shining even without spooling.

I would rather say they are *more* resistant to shoe-shining - if your 
drive can write up to 150 MB/s and throttle down to 80 MB/s you will 
still see shoe-shining if you only get backup throughput of 50 MB/s.

Arno

>>> --john
>>>
>>> Ryan Novosielski wrote:
>>> Arno Lehmann wrote:
>>>
> 
> Ildefonso Camargo
> 
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-- 
Arno Lehmann
IT-Service Lehmann
Sandstr. 6, 49080 Osnabrück
www.its-lehmann.de

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