[Help-tar] tar to DDS4 tape - small capacity

[Gaspar Bakos]

Hi,

I encounter a problem when writing to DDS4 tapes under Linux: I can write
far less (sometimes 10Gb) than the nominal capacity (20Gb) in uncompressed
mode. I was wondering if anyone has a clue where the error could be.
Basically the tar exits as:

-rw-rw-r-- hatuser/hatuser 5694575 2003-11-10 11:15:01 6-20031107/15641.fits.fgz
tar: /dev/nst0: Wrote only 0 of 10240 bytes
tar: Error is not recoverable: exiting now

$ echo $?
2


Q1: Is there a debug mode of tar, where it tells exactly why it failed?

After the error occurs, I don't see EOT or EOD with "mt status". But I
have the suspicion that the tape might be at the end. Unfortunately, if
I eject it to check what is going on, it automatically rewinds itself.
This might be related to
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=79027


Q2: BTW, does anyone know of a list that deals with archiving, or maybe
more specific: archiving to tape drives?

Any advice regarding the following (blocksizes, the way I archive, etc.)
are welcome.

Thanks
Gaspar

Software
--------
Linux redhat 7.3
kernel 2.4.18
mt-st v. 0.7
tar (GNU tar) 1.13.25
Adaptec AIC7xxx driver version: 6.2.4
aic7892: Ultra160 Wide Channel A, SCSI Id=7, 32/253 SCBs

Hardware
--------
Drive: Seagate STD6401LW-S DDS4 external DAT
Host: scsi0 Channel: 00 Id: 02 Lun: 00
  Vendor: SEAGATE  Model: DAT    9SP40-000 Rev: 9100
  Type:   Sequential-Access                ANSI SCSI revision: 03

Tape: Sony premium 150P DDS4


The way I archive:
------------------

mt -f /dev/nst0 rewind
tar cvf /dev/nst0 --totals -v -b 126 DIR1
tar cvf /dev/nst0 --totals -v -b 126 DIR2
...
tar cvf /dev/nst0 --totals -v -b 126 DIRN

Size of one DIR is typically 1.5Gb with du -s -k.
The files in DIR are 8Mb and few kB (large and small ones, alternating).

Stinit.def (I am using mode1)
----------

manufacturer=SEAGATE model="DAT    9SP40-000" revision="9100" {
scsi2logical=1
can-bsr can-partitions auto-lock
#
#modes
mode1 blocksize=0 compression=0
mode2 blocksize=512 compression=0
mode3 blocksize=0 compression=1
mode4 blocksize=512 compression=1
}

Some further questions

- Can archiving capacity crucially depend on
type of tape
retensioning
cleaning heads?

- Is there a way to tell how much length from the tape we actually
  consumed up at a given point?