Re: [Bug-tar] use optimal file system block size

[Joerg Schilling]

Christian Krause <address@hidden> wrote:

> Dear tar Community,
>
> We are using **tar** at our High-Performance Computing (HPC) at our research 
> institute iDiv. The networked file system serving (scientific) data on our 
> cluster is using a block size of 2 MiB:
>
> ```
> $ mkdir data
> $ dd if=/dev/zero bs=2M count=42 of=data/blob status=none
> $ stat -c %o data/blob
> 2097152
> ```
>
> **tar** does not explicitly use the block size of the file system where the 
> files are located, but, for a reason I don't know (feel free to educate me), 
> 10 KiB:

If you like to stay with the default tape block size, you cannot easily change 
this without a complete rewrite of the gtar source. If you however just change 
the tape block size, this may result in tapes that will not be readable on 
other hardware.

Star did this rewrite nearly 30 years ago, but it is done by implementing a 
ring buffer of configurable size. If you have e.g. a fast tape drive, you may 
use the option fs=512m to configure a 512 MB ring buffer or even much more, 
the default size is 8 MB. 

If there is still space in the ring buffer, star may read files with a single
read(2) system call. The tape block size is completely independent from the 
ring buffer size and this is one reason why star is very fast.

 


Jörg

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