RE: Avg Dump Rate and Compression
2004-03-24 01:37:16
> >yup. anyway, compression is off now (and was already set to none
> > when I sent this one).
>
> Drive hardware compression usually has a mind of its own. In
> particular, many drives look at the header, and set the compression
> on if the tape has ever been written to with the compression turned
> on, and there is nothing amanda can do about fixing that. Many
> drives have an indicator on the front panel called "dc", and if its
> lit while the tape is being written, then the compression is on.
>
> The only way I know of to fix such a tape is:
> rewind it
> read out the label to a scratch file using dd
> rewind it again
> turn the compression off with "mt -f device whatever turns it off"
> dd that scratch file back to the tape using the non-rewinding device
> dd at least enough data from /dev/zero to force the drive to
> flush its
> buffers. This will force the drive to turn the header compression
> flag off and that tape will not be compressed again unless you turn
> compression back on.
>
> I noted in a previous msg that your drive is a DDS3. This drive
> should be able to stream about 700k/second. I'd concur that the
> holding disk isn't enabled, or is somehow miss-configured and that
> the drive is shoe-shineing the tape due to running out of data and
> having to back up and restart once the buffer is up to 50% full or
> so. Thats a speed killer in addition to causing a lot of wear and
> tear on both the tape and the headwheel with all that starting and
> stopping that we suspect it may be doing.
I created a different configuration to backup a remote box, just to make
sure it could me better, and have a look at the results:
STATISTICS:
Total Full Daily
-------- -------- --------
Estimate Time (hrs:min) 0:00
Run Time (hrs:min) 0:11
Dump Time (hrs:min) 0:06 0:06 0:00
Output Size (meg) 317.0 317.0 0.0
Original Size (meg) 317.0 317.0 0.0
Avg Compressed Size (%) -- -- --
Filesystems Dumped 1 1 0
Avg Dump Rate (k/s) 870.2 870.2 --
Tape Time (hrs:min) 0:04 0:04 0:00
Tape Size (meg) 317.0 317.0 0.0
Tape Used (%) 2.7 2.7 0.0
Filesystems Taped 1 1 0
Avg Tp Write Rate (k/s) 1249.0 1249.0 --
USAGE BY TAPE:
Label Time Size % Nb
fenestra01 0:04 317.0 2.7 1
DUMP SUMMARY:
DUMPER STATS TAPER STATS
HOSTNAME DISK L ORIG-KB OUT-KB COMP% MMM:SS KB/s MMM:SS KB/s
-------------------------- --------------------------------- ------------
arara /root 0 324630 324630 -- 6:13 870.2 4:201249.0
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