tar's default block size & shoe-shinning

[Cyrille Bollu]

Hi all,

Could someone tell me if there are any possibilities to change the block size tar is using when backuping with amanda?

I'm asking this because we have recently bought an IBM ULTRIUM-TD3 LTO3 drive here and Amanda reports an average write rate of only 17MB/s (when the maximum speed should be 40 MB/s uncompressed). Which most probably means that the drive is shoe-shinning...

I think, tar's default block size of 10k is the most limiting factor since the constructor recommends a block size of 64kb and tests with "dd" reported a transfer speed of 33MB/s with bs=64k and only reports a 25MB/s with bs=10k.

I'm using amanda-2.4.4p1-0.3E (Red Hat ES 3.3).

Best regards,

Cyrille Bollu

=================================

Here are the full results from my "dd" tests:

bs          time (sec)      calculated speed (MB/s)
===================================
64k                   95                                   33,7
32k                 100                                   32
10k                 130                                   24,6
4k                   173                                   18,5
1k                   409                                    7,8

(results from the command "time dd if=/dev/sda2 of=/dev/nst0 bs=<var1> count=<var2>". Where <var2> is calculated so that <var1>*<var2>=3200MB)