Re: Couple of questions regarding dar

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

On 16/05/2020 16:52, Nils Privat wrote:
[...]
> I will see how to adapt/enhance dar_split to let you specify more 
> parameters there like a block size per system read/write call. The 
> work done by mbuffer is perturbed by dar_split except the rate (-R 
> option) at which data is sent.
> 
> 
>> Awesome, thanks. What exactly do you mean with "perturbed"? I
>> though mbuffer between dar and dar_split does not hurt?!

the fact mbuffer does not hurt does not mean it does nothing:

dar_split gather the regular flows of bytes mbuffer send by group of I
guess 2 MBytes (this depends on the system), but dar_split may receive
larger blocks from the system (SSIZE_MAX value) and send to tape this
amount at once. This is in that sense, what I mean telling dar_split
perturbes the work of mbuffer. But the byte rate received by the tape
is globally the same as it is limited by mbuffer, though it instead of
receiving it by block of 2 MB it receive larger blocks less often.

for that reason, I've enhanced dar_split for it takes some of the
features brought by mbuffer (block size and byte rate) when sending to
the final destination (here tapes). mbuffer can do much more than
that, so dar_split is not a replacement to mbuffer in all situations
but can work in conjunction with it as you did.

>> The reason i use mbuffer is because '-P 80 -m 8G', so that the
>> mbuffer can fill up a big buffer so that dar_split gets an
>> continuous stream to write ( i am using dar's encryption and
>> compression, which is sometimes slower than write speed to tape,
>> so with mbuffer i can buffer it). Do you dont recommend using
>> it?

I do not recommend not using it nor using it. This is completely
transparent to dar and dar_split, but as it seems, not to your tape
device.

[...]

Cheers,
Denis
-----BEGIN PGP SIGNATURE-----
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=ZF+K
-----END PGP SIGNATURE-----