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Hello Kern,
the problem is not so much the risk of errors, but that btape (and
correspondingly, Bacula) fails even the simplest of readback tests with
block sizes above 128KB. dd works perfectly well with multi-megabyte blocks,
both reading and writing.
Here's the info I previously collected:
btape cannot reliably handle anything larger than 128 KB (fails on reading,
see below).
However, when I read (using dd) the tape that btape supposedly has written
_two_ files of 10000 blocks each (and then fails after reading 3616 of
them!), dd reads read _each_ of btape-written 10000-block ``files'' as
_three_ separate actual tape files (of 3616+3616+2768=10000 blocks). Note
that this specific test was performed with a block size of 512KB (see Device
definition from bacula-sd.conf, below).
So, this might actually be a Bacula-specific problem after all. We see this
behavior consistently on two different HP LTO-5 drives, on two different SAS
HBAs (one using mpt2sas as driver, the other one with mvsas), and using two
different SAS cables.
If you need additional info, please let me know how to proceed.
Many thanks in advance,
Andreas
*** TRY BTAPE TEST, WILL FAIL ON READBACK
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
*** NOW READ BTAPE-WRITTEN TAPE USING DD
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
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