Mingus Dew wrote:
> All,
>      I apologize if this is a rehash of previous threads. I've tried
> searching the archives for an answer, but am not fully understanding
> what this means for me.
>
> I am running Bacula 2.4.2 on Solaris 10_x86. I am using an Exabyte
> Magnum 224 tape library with IBM Ultrium LTO-3 tape drive. I currently
> have Bacula configured for variable block sizes.
> I have been unable to determine or set a default blocking factor or
> compression on my tape unit. I do however believe that this unit accepts
> the configuration of the application. I don't know if Bacula, other than
> by using the /dev/rmt/0cbn device purposefully sets compression. I am
> under the impression however that Bacula is using its default block size
> of 65k.
>
> I have been having problems with tape backups taking much longer than I
> believe they should. I have not yet had to restore from tape and have
> only done so in testing. In production I have a couple of jobs with
> these properties
>
> Job1 - 334G to tape - Avg 26.20 Mbytes/sec
> Job2 - 1.6T to tape - Avg 13.74 Mbytes/sec
>
> Since I've not figured out if Bacula will tell me the write speed to
> tape for the job, I've just used the start and end times along with the
> amount of data to calculate the speed. This does not take into account
> the time required to spool data. I've turned off data spooling for Job2
> in order to compare after this week's run and see what the speed might be.
>
> Testing with tar has shown that using the 65k block size is definitely a
> performance bottleneck. I used real data (not empty or mkfile generated)
> for my testing to accurately represent what I usually put to tape
> (Oracle RMAN backup files).
>
> Here are the numbers:
>
> block size 65 Kbytes
> Test #1 (backup) tar > rmt/0cbn - 85 Mb/s
> Test #2 (restore) tar > rmt/0cbn - 42 Mb/s
>
> This is similar, though still faster to what I see for Bacula jobs. I
> think the difference is in the data spooling.
>
> Block size 1024 Kbytes
> Test #1 tar > rmt/0cbn - 410 Mb/s
> Test #2 tar > rmt/0cbn - 409 Mb/s
>
> Block size 2048 Kbytes
> Test #1 tar > rmt/0cbn - 410 Mb/s
> Test #2 tar > rmt/0cbn - 408 Mb/s
>
> With these other tests and a much larger blocking factor I see greatly
> improved performance.
>
> I can tell that I need to change the blocking factor for bacula.
> However, I'm very confused by the documentation's description of doing
> so and the consequences. I'd like to know how I should setup my blocking
> factor so that Bacula uses the tape drive most efficiently and also if I
> change the blocking factor, how will it affect jobs I currently have on
> tape or labeled volumes?
>

Aside from the Bacula stuff, I'm interested in those 410Mb/sec data
rates you have listed above. According to IBM's website, the max data
rate for their LTO-3 drive is 120MBytes/sec. What exactly are you
tarring to achieve 410Mbtyes/sec? (assuming your 410Mb/sec means
Mbytes/sec). If you are tarring a file full of zeros, this will be
compressing extremely well and will be giving you misleading transfer
rates. I get no better than 105Mbytes/sec on an LTO-4 with tar, however
big I make the blocksize.

Bacula has given me no better than 80MBytes/sec on to this LTO-4 drive
with a blocksize of 256K, and doesnt improve on this with bigger block
sizes.

Cheers,
Terry


> Thank you,
> Shon
>
>
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