On Thursday 20 September 2007 11:33, Marc Schiffbauer wrote:
> * Kern Sibbald schrieb am 20.09.07 um 11:07 Uhr:
> > On Thursday 20 September 2007 00:59, Arno Lehmann wrote:
> > > Hi,
> > >
> > > 18.09.2007 16:25,, Marc Schiffbauer wrote::
> > > > * Chris Howells schrieb am 18.09.07 um 16:14 Uhr:
> > > >> Hi,
> > > >>
> > > >> Marc Schiffbauer wrote:
> > > >>
> > > >> Finally got around to messing around with bacula again...
> > > >>
> > > >>> The manual says that nnn being the same number for both settings
> > > >>> means "fixed" blocksize.
> > > >>>
> > > >>> As I understand it, your solutions should be to just set the
> > > >>> "Minimum Block Size" so you get a good perfromance.
> > > >>>
> > > >>> Minimum Block Size = 1048576
> > > >>
> > > >> Unfortunately just setting a Minimum Block Size does not work. btape
> > > >> for instance will not work then. It dies with a glibc error. (See
> > > >> end of mail for full trace.
> > >
> > > Interesting. On a FreeBSD 7 system with Bacula 2.2.4 btape crashes
> > > when I use larger block sizes. I haven't found the actual limit, but
> > > 512k blocks work, 1MB sized ones don't.
> >
> > Bacula currently limits block sizes to 1MB. This limit was implemented 7
> > years ago when the fastest drive was a DLT. I will increase the size,
> > but I am quite skeptical about writing block sizes of 1 or 2 Megabytes.
> > I believe that you may get a bit more speed, but you will probably
> > increase the rate of errors -- unless drive technology has progressed
> > more than I am aware of.
>
> I never heard of such errors in current (enterprise) drives that
> depend on the blocksize being too large.
>
> Other commercial enterprise backup solutions do reliable backups
> with maximum drive speed, so this seems not to be a problem. If it was I
> would call this crappy hardware.
There are and will be people doing backups on DDS drives for quite a long
time. I personally would not use one for production (I use one for testing),
but I would not call it crappy hardware. However, you are very unlikely to
get DDS drives to work with anything bigger than 128K blocks.
>
> The thing is if bacula is too slow in writing to tapes this might be a
> showstopper for large environments because this a) wears the drive
> ("shoe-shining") and b) will make backups run way too long.
I think Ralf has shown that Bacula is not too slow writing tapes with the
default size. I don't say that it couldn't be faster, but when it comes to
backups, I am not a cowboy. I believe in being conservative and doing *very*
careful testing.
In any case, you currently have the ability with unmodified Bacula code to
block up to 1MB, and since it is Open Source, you can always push that as
high as you want or remove even the restriction all together.
>
> Why do you limit the blocksize at all?
Insanity check to keep the user from shooting himself in the foot.
> I suggest setting a
> reasonable default, but let it to the user to configure blocksizes
> whichever she wants. This way bacula will be fit for future
> drives... maybe we have drives with blocksizes of 20MB or 30MB in a
> few years...
Yes, then we will increase it.
>
> > By the way, increasing the Minimum Block Size is NOT the way to increase
> > the Maximum block size. In general one should *never* set the minimum
> > block size unless you have an older brain damaged drive. In increasing
> > the Minimum Block Size, you virtually guarantee to waste tape for no good
> > reason. The way to increase the maximum block size is to use the Maximum
> > Block Size directive, which I previously thought was rather obvious ...
> > oh well.
>
> It is, at least to me. But the thing was to really increase the
> minimum blocksize to increase speed.
>
> Where is this wasting space? If you write 200GB to a tape and the
> last block is only one byte in size you have wasted nearly 2MB of
> space, right?
Well, the minimum Bacula block size is about 112 bytes, which will be rounded
up to the system min block size, which I think is 1024 bytes (perhaps 512).
There is no need to specify a minimum block size, and if you do, you will
have wasted *many* multiples of 2MB on most volumes for no good reason so why
do it? Bacula will always try to use the Maximum Block Size if it can.
>
> -Marc
-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2005.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
_______________________________________________
Bacula-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/bacula-devel
