Bacula-users

Re: [Bacula-users] Is anyone using >128K blocks with LTO-4 or LTO-5 drives?

2013-09-17 12:47:13
Subject: Re: [Bacula-users] Is anyone using >128K blocks with LTO-4 or LTO-5 drives?
From: Kern Sibbald <kern AT sibbald DOT com>
To: Andreas Koch <koch AT esa.informatik.tu-darmstadt DOT de>
Date: Tue, 17 Sep 2013 18:42:58 +0200
What version of Bacula (btape) are you using?

There was a logic error in btape that stopped reading after
a certain number of bytes, because the first versions never
expected to have a different block size.  It seems to me that
I fixed that long ago though.

Best regards,
Kern

On 09/17/2013 03:53 PM, Andreas Koch wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> 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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