On Mon, Oct 06, 2003 at 04:49:27AM +0100, Tony wrote:
> Hi,
> 
> I am using Amanda to back up 4 machines to a 20/40 DDS4 (DAT)
> tape in one of the machines. I am doing a full backup every
> night as there is not a lot of data on all of the machines (they
> are application servers, with not much data storage). As always
> the backup size increases over time. Up until recently
> everything has been going fine. Now I am getting errors that
> there is "no space left on device" when writing to tape. The
> thing that i am struggling to work out is why ? I am using
> software compression and Amanda reports that after compression,
> the output size is just over 15 GB (which should fit easily on a
> 20GB tape).
> 
> To further add to the confusion, I ran a "tapetype" to see what
> Amanda thought it could fit on the tape drive and the results it
> came back with were:
> 
> define tapetype testdds4 {
>     comment "just produced by tapetype program"
>     length 13565 mbytes
>     filemark 0 kbytes
>     speed 1842 kps
> }
> 
> which shows that Amanda thinks the tapes are only 13.5 GB (or
> thereabouts). This explains why the backup might be failing once
> it goes over this value.
> 
> When I installed Amanda, I read the doc that says that hardware
> compression is BAD and so should be turned off. The drive I have
> doesn't have any jumper settings for compression, so I can't
> turn it off there. I have never explicitly turned hardware
> compression ON with the software, so I kinda assumed that it
> wouldn't be doing hardware compression at all. From digging
> through the archives there appears to be evidence of the same
> happening to other people to support this theory.
> 
> So my question are:
> 
> 1. Is my diagnosis correct (tape drive is using hardware
> compression) ?
> 2. How can I tell if the drive is doing hardware compression ?
> 3. How can I stop the drive from doing HW compression ?
> 4. If this isn't the problem, I'm open to other suggestions.
> 
> 
> Many thanks,
> Tony.
> 
> =====================================
> 
> These dumps were to tape daily01wed.
> *** A TAPE ERROR OCCURRED: [[writing file: No space left on
> device]].
> Some dumps may have been left in the holding disk.
> Run amflush to flush them to tape.
> The next tape Amanda expects to use is: daily04mon.
> 
> FAILURE AND STRANGE DUMP SUMMARY:
>   wonderwoma /var lev 0 STRANGE
>   qtechwas0  /var lev 0 STRANGE
>   qtechwas1  /opt lev 0 STRANGE
>   qtechwas2  /opt lev 0 FAILED [out of tape]
> 
> 
> STATISTICS:
>                           Total       Full      Daily
>                         --------   --------   --------
> Estimate Time (hrs:min)    0:03
> Run Time (hrs:min)         3:12
> Dump Time (hrs:min)        2:20       2:20       0:00
> Output Size (meg)       15366.2    15366.2        0.0
> Original Size (meg)     25498.3    25498.3        0.0
> Avg Compressed Size (%)    60.3       60.3        -- 
> Filesystems Dumped           29         29          0
> Avg Dump Rate (k/s)      1878.7     1878.7        -- 
> 
> Tape Time (hrs:min)        1:45       1:45       0:00
> Tape Size (meg)         11753.6    11753.6        0.0
> Tape Used (%)              59.0       59.0        0.0
> Filesystems Taped            28         28          0
> Avg Tp Write Rate (k/s)  1909.3     1909.3        -- 
> 
> 
> NOTES:
>   taper: tape daily01wed kb 14775776 fm 29 writing file: No
> space left on device
>   driver: going into degraded mode because of tape error.
> 

That looks to be the problem, unless ???
I'm surprised HW compression expands it that much.

You are using DDS-4 tapes, not DDS-{123} ones right?

Try it next run without software compression.  25GB should have
no trouble fitting.  HW compression will take it down to about
the same 15GB that gzip did.

I think some mt versions have commands that show the compression
state.  And commands to turn it off too.

Most drives would come with compression on as the default.

My drive (HP DDS-3) has DIP switches affect the defaults.
One controls which state it comes up in after at power up.
The other says whether it can subsequently be changed by
a software command.  For a while I did not think it had
any switches or jumpers to affect compression.  Then I
found out you have to remove the drive from the case to
access them.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
 4455 Province Line Road        (609) 252-0159
 Princeton, NJ  08540-4322      (609) 683-7220 (fax)