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.
>> For instance with the following setting:
>>
>> Minimum Block Size = 256000
>>
>> [EMAIL PROTECTED]:/etc/bacula# btape -c bacula-sd.conf /dev/nst0
>> <snip>
>> test
>> <snip>
>> *** glibc detected *** malloc(): memory corruption: 0x080d9d90 ***
>>
>> Setting both a Minimum Block Size and Maximum Block Size to the same
>> value *does* seems to work with btape.
>>
>> BTW, I tried using 1048576. Unfortunately this does not work. From
>> src/stored/dev.c:
>>
>> if (dev->max_block_size > 1000000) {
>> Jmsg3(jcr, M_ERROR, 0, _("Block size %u on device %s is too
>> large, using default %u\n"),
>> dev->max_block_size, dev->print_name(), DEFAULT_BLOCK_SIZE);
>>
>> Oops.
>>
>> Why can I not use > 1000000 bytes? This seems a *really* strange
>> restriction. I can happily use blocks of several megabytes using tar.
For current tape drives, we really need to support larger block sizes.
I tested today with an AIT-5 tape drive.
Throughput measured with dd, test file 8 GB in size, so I think we can
ignore the effects of buffering and caches.
disk -> /dev/null ~60MB/s
disk -> tape, <64kB blocks: ~5MB/s
1 MB blocks: ~15MB/s
2 MB blocks: ~20MB/s (close enough to the published
specification)
Unfortunately, I could not test with 512k block sizes in btape - there
were positioning errors during the test, while the default block sizes
worked flawless. I don't know if more in-depth testing is possible as
this is a customer's system which should go into production some day soon.
Anyway, for decent performance, on that system block sizes well beyon
1MB should be used.
System is FreeBSD 7-current, AIT-5 tape drive in autochanger, 2GB RAM,
and a reasonable disk subsystem. (Again, I don't have many details
now, might get them later, but the key issue here is that Bacula
should support larger tape block sizes.)
> Indeed.
> I discuss that on the devel list and/or maybe open a
> bugreport in the bacula BTS.
>
> And btape crashing is a bug as well...
Yes...
> -Marc
Arno
--
Arno Lehmann
IT-Service Lehmann
www.its-lehmann.de
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