sa(4) 9.2->10.1, nsa0.0: request ptr 0x803135040 is not on a page boundary; cannot split request

[Harald Schmalzbauer]

 Hello,

I read about the changes in sa(4) regarding large-block-split changes
and the transitional 'kern.cam.sa.allow_io_split' workarround.

I'm using bacula (7.0.5) and my previous neccessarry multi-blocking
adjustmets like "Minimum block size = 2097152" obviously didn't work
with FreebSD 10.1 anymore.
Good news is, they are not needed any more!
With the default of 126 blocks (64512) I get 60-140MB/s with btape(8)'s
speed test on my LTO4 (HH) drive and another quick test showed that
using mbuffer(1) for zfs(8) 'send' isn't needed anymore (| dd
of=/dev/nsa0 bs=64512 seems to max out LTO4 speed). [with FreeBSD 9 the
transfer rates were some magnitudes lower with these block size settings!]

Not so good news is, that bacula can't read the tape's label.
'Labeling a tape (with 'label' at bconsole(8) or btape(8)) is
successful, and btape(8)'s 'readlabel' partially displays the correct
label, but not the very beginning of the label:
Volume Label:
Id : **error**VerNo
…rest OK

While it should read:
Volume Label:
Id : Bacula 1.0 immortal
VerNo : 11
…

When btape(8) starts to read the label, the _subject's error is reported_:
*nsa0.0: request ptr 0x803135040 is not on a page boundary; cannot split
request*

The same error show up if I configure bacula to use a fixed block size
of kern.cam.sa.0.maxio (131072).


Like expected, allowing split (with kern.cam.sa.allow_io_split in
loader.conf) works arround that problem.
But I'd like to understand why I cannot set kern.cam.sa.0.maxio resp.
why btape(8) doesn't work 100% correct although blocksize < sa.0.maxio

I don't have enough understanding to check the code myself, if it's a
cam/sa(4) issue in FreeBSD or a problem in btape(8) (and also bacula
itself, most likely the tool shares the code with bacula's storage deamon).

Any hints highly appreciated!

Thanks,

-Harry


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