Re: Tape throughput for Sony AIT-3

John Doe <john_at_doe.com> wrote:
>I am trying to backup the database using Sony SDX-700C AIT-3 drive. When I
>test the drive speed with
>
>dd if=/dev/zero of=/dev/rmt/0un bs=128k count=8192,
>
>I get a throughput of 18MB/sec.
>
>But when I 'tar' a Oracle datafile onto the tape, I get a pathetic
>throughput of 5MB/sec.
>
>Why the drastic drop? I know Oracle datafile probably dont compress well,
>but I still expect to get the uncompressed spec'd rating for the drive which
>is 12MB/sec.
>
>Any help appreciated.

tar may well be writing in 512 byte blocks, rather than the 128kB blocks you used in the dd test - what throughput do you get if you dd with a 512 byte block?

If this is the case, you might be able to pipe tar into dd with "ibs" and "obs" to write to the tape in larger blocks.

Er.... and if I'm barking up the wrong tree, you might get better answers from a Unix/sysadmin type newsgroup than an Oracle/DBA type newsgroup. There's nothing special about Oracle datafiles from the Unix point-of-view.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/