svn commit: r344562 - head/sys/ufs/ffs

[Rodney W. Grimes]

> On Mon, 25 Feb 2019, Jason Harmening wrote:
> 
> > On 2/25/19 9:46 PM, Bruce Evans wrote:
> >> 
> >> block_size <= PAGE_SIZE is very uncommon for ffs, even on systems with 
> >> large
> >> pages.  MINBSIZE is 4096 in ffs (except in my version, it is 512).  The
> >> default is 32768 in newfs.  I consider this excessive and only use it for
> >> file systems with many files larger than 1GB, but it is the most common 
> >> size.
> >> It is larger than the large page size of 8192.
> >
> > I think this is a case of filesystem logical block size vs. media sector 
> > size, right?  Here we're checking the devvp's block size, which I think 
> > should correspond to the sector size.  I'd expect cases of that being
> > greater than PAGE_SIZE to be uncommon, in fact geli warns when that is the 
> > case.   I probably should've made that clearer in the commit message.
> 
> Yes, I missed that you are checking devvp.  ffs_getpages() also checks
> devvp.
> 
> So the bug has nothing to do with file system logical (fragment) or i/o
> (block) block size's, except file systems themselves won't work unless
> their i/o size is a multiple of the underlying devices (sector) i/o size.
> 
> Are there physical disk with sector size > PAGE_SIZE now?

I have been told that there are some sd/flash devices that
have a 16k physical sector size, I have not been able to
confirm that information though.

> It is easy to
> create virtual (md) disks with sector size > PAGE_SIZE, and this may even
> be useful for avoiding the related problem of having to access large fs
> blocks to do i/o to small md sectors.  I think it is best to use PAGE_SIZE
> blocks in all layers and sometimes combine these into clusters.
> 
> Bruce
-- 
Rod Grimes                                                 rgrimes at freebsd.org