Zitat von Dan Langille <dan AT langille DOT org>:

> On 2012-08-21 05:42, Alan Brown wrote:
>> On 21/08/12 08:37, lst_hoe02 AT kwsoft DOT de wrote:
>>> Some short tests with the "Maximum Block Size" set, show transfer
>>> speed to the LTO-4 of 87MBytes/sec with 256K and 98MBytes/sec with 1M
>>> with Bacula encrypted data, so with this we are reaching the
>>> theoretical uncompressed speed of the LTO-4 device by ~20%. It would
>>> be really helpful if there is some developer to say if there is any
>>> downside of large block sizes?
>>
>> I'm not a dev, however I use 2Mb block size (this is the largest bacula
>> currently supports)
>
> I suspect I'm an edge case with tape.  I'm using old technology and old
> hardware.  That's what I can afford on a home network.
>
> I wasn't sure what block size I'm using on my DLT-7000 tape library, but
> I see it's variable....
>
> $ sudo mt -f /dev/nsa0 status
> Mode      Density              Blocksize      bpi      Compression
> Current:  0x1b:DLTapeIV(35GB)    variable       85937    IDRC
> ---------available modes---------
> 0:        0x1b:DLTapeIV(35GB)    variable       85937    IDRC
> 1:        0x1b:DLTapeIV(35GB)    variable       85937    IDRC
> 2:        0x1b:DLTapeIV(35GB)    variable       85937    IDRC
> 3:        0x1b:DLTapeIV(35GB)    variable       85937    IDRC
> ---------------------------------
> Current Driver State: at rest.
> ---------------------------------
> File Number: 0  Record Number: 0        Residual Count 0
>
> All my tape jobs involve data on local HDD.  That is, I backup to  
> disk first, then
> copy to tape.  The HDD and the tape are both connected to the same bacula-sd.
>
>> The only downside is that you _must_ mark all active tapes as "used"
>> before changing block size.
>
> Setting them as USED is fine by me.  I write my tapes until they are FULL.
> Checking the recycling algorithm documentation[1], this will not affect
> pruning.
>
>> Bacula will be able to read the old tapes, but it cannot handle maximum
>> block size changing midway through a tape.
>
> I found one reference[2] after a bunch of searching, but I should look more:
>
> ###
> The DLT drive default data block transfer size is 4KB (4096 bytes).
> To achieve better performance, adjust block size to 32K bytes or
> higher when using a fixed block device.
> ###
>
> My full backups, roughly 90GB, take about 12 hours to copy to tape.  Thus,
> my only incentive to change blocksize is to avoid shoe-shine, which I do not
> think is happening at present.

That's around 2MByte/sec?
Even DLT-7000 should do better, according to wikipedia it should be  
able to do around 5MByte/sec.

BTW: Do you need some Hardware? We have a Overland LXB Powerloader  
(DLT-8000) near the dustbin ;-)

Regards

Andreas



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