Hi Jeremy,
On Fri, Jun 04, 2004 at 04:15:27PM -0400, Jeremy Jackson wrote:
> Hi,
>
> I'm reading xfsdump/common/drive_scsitape.c:calc_best_blk_and_rec_sz()
> and it seems that the manual page is inaccurate regarding the -b switch.
>
> It indicated a 1MiB default, but reading the code, it looks like if -m
> is not used and if -b is not used, and the device is a local (not rmt)
> tape device, then the block size defaults to the lesser of the drive's
> maximum blocksize, or STAPE_MAX_RECSZ
>
I reckon the code is a bit messy here.
I believe the man page is correct, however.
STAPE_MAX_RECSZ is 2MiB which was used on IRIX.
STAPE_MAX_LINUX_RECSZ is 1MiB for use on Linux.
And dc_maxblksz comes from mtinfo.maxblksz which comes from
STAPE_MAX_LINUX_RECSZ.
From memory linux st driver didn't support maxblksz as was the case
with the IRIX driver (only a MT_ST_BLKSIZE_SHIFT on the mt_dsreg).
We used 1MiB for Linux b/c Linux often Linux couldn't handle 2MiB.
In recent times it was pointed out that for Linux a smaller record
size than 1MiB would still give good performance.
> A description of tape records (vs tape blocks) would be helpful also.
>
In xfsdump/doc/xfsdump.html at the end, I was wondering the same question :)
--Tim
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