Breifly, the new superblock layout increases the size of some fields
and removes support for rotationally optimized block allocation, which
is not useful on modern disks.

The advantages on an FFSv1 filesystem are few, although the changes
are important when using an FFSv2 filesystem which can support disks
with larger than 2^32 worth of blocks.

It is not particularly necessary to upgrade your FFSv1 superblock,
since the kernel can now use either the old style superblock
under compatibility mode or the new style superblock.  New filesystems
are now created with the new style superblock by default.  However,
netbsd 1.6 can only use the old style superblock.

Before the recently added compatibility mode was supported, the kernel
would automatically upgrade your superblock, which would cause
problems for older systems.  This would only affect users who were
running -current sources between April and December of 2003.

Currently, it is not easily possible to downgrade the superblock to
the old style.  If I get some spare time, I would like to add a
downgrade option to fsck_ffs and newfs to assist people who need to
create filesystems that need to be used on older versions of netbsd.
Until then, people who need to share filesystems with older versions
of netbsd should create their filesystems under netbsd 1.6 and should
not upgrade them using fsck_ffs -c 4.

Darrin

Pavel Cahyna <pavel.cahyna@st.ms.mff.cuni.cz> writes:

> Hello,
> 
> please, what are the differences and advantages of the new FFS superblock
> layout (compared to the old one)?
> 
> Bye	Pavel