Subject: Re: Reading DLT does not stream?
To: Felix Deichmann <>
From: Jukka Marin <>
List: netbsd-users
Date: 09/02/2004 21:21:38
On Thu, Sep 02, 2004 at 05:47:10PM +0200, Felix Deichmann wrote:
> Is it possible that the streamer's cache is NOT enabled?

I would think that would affect writes as well?

> An excerpt from the DLT FAQ
> (

I'll check these URLs.

> A second possibility is the record size being used by the host.
> The DLT 2000 is especially sensitive to record size.  In general,
> the bigger, the better.  We recommend 32K, or even 64KB records
> if possible (up to 16MB records are supported).  In general,
> any record size greater than 8KB should result in a
> bottleneck-free tape drive.  Any record size less than 8KB will
> give performance problems.  Many software packages default to
> 512 byte records.  This will result in throughput in the
> 100-200 KB/sec range.

I think I used 10k for writing (buffer size set to buffer command).

> Jukka, have you double-checked that the disk is fast enough concerning 
> writes?

Absolutely.  I used a 10 MB buffer between tar and the tape and reading
the actual file off disk looks like this:

# dd if=foo.tgz of=/dev/null bs=1m
23640+1 records in
23640+1 records out
24788417513 bytes transferred in 684.733 secs (36201581 bytes/sec)

In addition, I was sitting here while writing the tape and the drive was
streaming all the time.  When reading, it _never_ streams, even when
writing the data to /dev/null.