Hello Dan,
Copying from disk to tape with Bacula's current algorithm is virtually
guaranteed to be slower than using tar. This is for several reasons:
1. Bacula currently is single threaded and reads a block from disk then
stops to write the output block to tape.
2. After reading the block from disk, Bacula checks the checksum (CPU
intensive).
3. After the checksum is verified, Bacula reads each record from the
block and then packs the records into a new block for writing.
4. Once the output block is full, Bacula computes a checksum for the
block, writes it and waits for the I/O to be complete.
So, as you can see, it is a very expensive process, but it is the only
way to guarantee that the whole prior backup is properly copied.
I have not tried this, but one thing that may help a lot is to turn on
data spooling for the tape device. This will probably not speed up the
process but should prevent that tape shoe-shine (start and stopping).
At some later time, Bacula will have multiple threads -- one that reads
and one that writes, and this could drastically improve performance.
Best regards
Kern
On 03/11/2016 08:44 AM, Dan Langille wrote:
>> On Mar 9, 2016, at 6:52 PM, Heitor Faria <heitor AT bacula.com DOT br> wrote:
>>
>> I have a copy to tape job which copies from disk to tape using Bacula 7.4.0
>> and PostgreSQL 9.4 on FreeBSD 10.2
>>
>> Everything is within one SD
>>
>> Full details at https://gist.github.com/dlangille/2341a6da8f9ee836270c
>>
>> The job summary:
>>
>> Start time: 09-Mar-2016 19:41:54
>> End time: 09-Mar-2016 20:51:02
>> Elapsed time: 1 hour 9 mins 8 secs
>> Priority: 410
>> SD Files Written: 1
>> SD Bytes Written: 52,897,660,928 (52.89 GB)
>> Rate: 12752.6 KB/s
>>
>> If I tar the volumes directly to tape, it takes only 16 minutes.
>>
>>
>> $ time sudo tar -cf /dev/nsa1 IncrAuto-4525 IncrAuto-4320 IncrAuto-4324
>> IncrAuto-4321 \
>>> IncrAuto-4055 IncrAuto-4322 IncrAuto-4319 IncrAuto-3969 IncrAuto-3972 \
>>> IncrAuto-3973 IncrAuto-3971 IncrAuto-4058
>>
>> real 15m47.508s
>> user 0m5.844s
>> sys 1m51.834s
>>
>> Spooling attributes is trivial:
>>
>> 09-Mar 20:51 crey-sd JobId 232945: Sending spooled attrs to the Director.
>> Despooling 321 bytes ...
>> 09-Mar 20:51 bacula-dir JobId 232944: Bacula bacula-dir 7.4.0 (16Jan16):
>>
>> I am not sure where to look to figure this out.
>> Hello, Dan: maybe there is nothing to figure it out. Packing volumes with
>> tar directly to tapes makes you unable to restore a single file or even a
>> single job (with bootstrap) from an entire tape. I think it's a trade-off.
>
> I have no desire to use tar.
>
> I have a desire to effectively use an LTO tape drive.
>
> --
> Dan Langille - BSDCan / PGCon
> dan AT langille DOT org
>
>
>
>
>
>
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