[Bacula-users] btape vs. dd: Strange behavior on LTO-5

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Hi all,

I am stumped by the behavior of an HP LTO-5 drive running on Scientific
Linux 6.4 (Kernel 2.6.32-358.14.1.el6.x86_64) and Bacula 5.2.12.
Specifically, using dd, I can read and write block sizes of 2 MB, but btape
cannot reliably handle anything larger than 128 KB (fails on reading, see
below).

However, when I read the tape that btape supposedly has written two files of
10000 blocks each (and then fails after reading 3616 of them) using dd, I
read each of btape-written 10000-block ``files'' as _three_ actual tape
files (of 3616+3616+2768=10000 blocks). Note that this test was performed
with a block size of 512KB (see Device definition from bacula-sd.conf, below).

I would be grateful for any ideas on how to resolve this. With the smaller
block sizes, the backup is noticeably slower for compressible data (e.g.,
database dumps), so I really would like to move back up to larger block sizes.

Many thanks in advance,
  Andreas Koch

gundabad ~ # btape -c /etc/bacula/bacula-sd.conf /dev/nst0
Tape block granularity is 1024 bytes.
btape: butil.c:290 Using device: "/dev/nst0" for writing.
btape: btape.c:477 open device "LTO-4" (/dev/nst0): OK
*test

=== Write, rewind, and re-read test ===

I'm going to write 10000 records and an EOF
then write 10000 records and an EOF, then rewind,
and re-read the data to verify that it is correct.

This is an *essential* feature ...

btape: btape.c:1157 Wrote 10000 blocks of 524188 bytes.
btape: btape.c:609 Wrote 1 EOF to "LTO-4" (/dev/nst0)
btape: btape.c:1173 Wrote 10000 blocks of 524188 bytes.
btape: btape.c:609 Wrote 1 EOF to "LTO-4" (/dev/nst0)
btape: btape.c:1215 Rewind OK.
Got EOF on tape.
btape: btape.c:1233 Read block 3617 failed! ERR=Success
*q
btape: smartall.c:404 Orphaned buffer: btape 280 bytes at 15e55e8 from jcr.c:362
gundabad ~ # mt -f /dev/nst0 rewind
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
3616+0 records in
3616+0 records out
1895825408 bytes (1.9 GB) copied, 3.7062 s, 512 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
3616+0 records in
3616+0 records out
1895825408 bytes (1.9 GB) copied, 3.7542 s, 505 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
2768+0 records in
2768+0 records out
1451229184 bytes (1.5 GB) copied, 2.88829 s, 502 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
3616+0 records in
3616+0 records out
1895825408 bytes (1.9 GB) copied, 3.75554 s, 505 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
3616+0 records in
3616+0 records out
1895825408 bytes (1.9 GB) copied, 3.75338 s, 505 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
2768+0 records in
2768+0 records out
1451229184 bytes (1.5 GB) copied, 2.88846 s, 502 MB/s
gundabad ~ # dd if=/dev/nst0 of=/dev/null bs=512k
0+0 records in
0+0 records out
0 bytes (0 B) copied, 0.247548 s, 0.0 kB/s

Device {
  Name = LTO-5
  Media Type = LTO-5
  Archive Device = /dev/nst0
  AutomaticMount = yes;               # when device opened, read it
  AlwaysOpen = yes;
  RemovableMedia = yes;
  RandomAccess = no;
  Maximum File Size = 8g;
  Minimum block size = 524288
  Maximum block size = 524288
  Changer Device = /dev/changer
  AutoChanger = yes
  # AHK we want to interrogate the drive, not the changer
  Alert Command = "sh -c 'smartctl -H -l error /dev/sg11'"
  Maximum Spool Size = 3000g
  Spool Directory = /etc/bacula/spooldisk/BaculaSpool
  Maximum Network Buffer Size = 65536
}


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