I have a disk formatted as follows.

Part Flag Tag Cylinders Size
===================================================
0 wm root 0 - 38125 26.18 Gb
1 wu swap 38126 - 49776 8 Gb
2 wm backup 0 – 49779 34.18 Gb
3 wm unassigned
4 wm unassigned
5 wm unassigned
6 wm unassigned
7 wm home 49777- 49779 2.11 Mb

Note none of the above slices have been mounted nor do they contain any data.

First question - what is the significance of the Tag's ? What does the root, backup and home tags signify ?

I want to reorganise the slices as such

Part Flag Tag Cylinders Size
=================================================
0 wm usr 0 - 38108 26.17 Gb
1 wu swap 38126 - 49776 8 Gb
2 wm backup 0 – 49779 34.18 Gb
3 wm unassigned 0 0
4 wm unassigned 0 0
5 wm unassigned 0 0
6 wm usr 38109 – 38125 11.95 Mb
7 wm home 49777- 49779 2.11 Mb

i.e. basically create Slice 6 with a bit of space previously belonging to Slice 7

I save the partition mapping. However when I try to recreate the filesystems for slices 6 & 7 ( using newfs /dev/rdsk/c0t1d0s6 and c0t1d0s7 ), Slice 7 completes ok but for Slice 6, I get the following :

warning inode blocks/cyl group (134) >= data blocks (90) in last cylinder group. This implies 1440 sector(s) cannot be allocated
/dev/rdsk/c0t1d0s6: 23040 sectors in 16 cylinders of 2 tracks

Even when I reorganise the entire disk to have contiguous use of Cylinders i.e.

Part Flag Tag Cylinders Size
==================================================
0 wm usr 0 - 38108 26.17 Gb
1 wm unassigned 0 0
2 wm backup 0 – 49779 34.18 Gb
3 wm unassigned 0 0
4 wm unassigned 0 0
5 wm unassigned 0 0
6 wm usr 38109 – 38125 11.95 Mb
7 wu swap 38126 – 49776 8Gb

and then use newfs to recreate the file system for Slices 6 & 7. Again the FS for Slice 7 creates ok but for Slice 6 I get the same error as before

warning inode blocks/cyl group (134) >= data blocks (90) in last cylinder group. This implies 1440 sector(s) cannot be allocated
/dev/rdsk/c0t0d0s6: 23040 sectors in 16 cylinders of 2 tracks, 720 sectors
11.2 MB in 1 cyl groups ( 16 c/g 11.25Mb/g, 5540 i/g )
Super-block backups ( for fsck –F ufs –o b=# ) at : 32,

Also When I use the MODIFY partition option under the FORMAT command, I get the warning :

Warning: overlapping partition (6) in table

I don't understand this, since clearly from my mappings above, the cylinders are not overlapping ?

Any idea of what is going on ?

Assuming you are using Solaris, after you change the partitions in format, do you label it before quitting out of format? It may be keeping some of the old info along with the new - only explaination I can think of.