Ditto Max Overrun Issues

Problem: Backups to a Ditto Max tape drive suffer for a large number of overruns causing "shoeshining," or tape stop/start repositioning, on a P5-166MHz system (or slower).

Nick Holloway Suggests the following:

I find I am not receiving ECC and CRC errors on a P133 (which is faster than the minimum spec listed in the system requirements on the Max box). In addition, the number of repositions is low.

There are a few things that I've done help this:

The first is to limit the data rate to 2000 (in /etc/conf.modules). Otherwise, ftape starts at the 4000Mb/s the accellerator can support, errors are reported and it backs off. Sometimes it only went down to 3000, but errors were reported, and the fifo threshold had to be increased. So, I stick to 2000Mb/s.

alias char-major-27 zftape
options ftape ft_fdc_driver=ftape-internal,none,none,none # ft_tracings=4
options ftape-internal ft_fdc_base=0x370 ft_fdc_irq=6 ft_fdc_dma=3 ft_fdc_rate_limit=2000
pre-install ftape-internal /sbin/swapout 16

Secondly, I found that enabling multi-sector transfer and interrupt unmasking for my IDE disk stopped the number of times the tape was repositioned during a backup. The usual warnings about using interrupt unmasking apply -- see hdparm manual page.

hdparm -u 1 -m 16 /dev/hda
hdparm -u 1 -m 16 /dev/hdb

Finally, I leave the machine otherwise idle when it is performing the backup. [editor's note: It's also best to run from console mode (no X11).]

As I remember it, the data rate reported by dump is ~160K/s.

Nick Holloway http://www.alfie.demon.co.uk/

Reprinted here with permission