hi there,

with the appropriate version of SQLServer you can do the rebuild with the ONLINE-option so there would not be any downtime. Otherwise use the REORGANIZE-command instead of the REBUILD.

REORGANIZE is much slower then REBUILD but is an online option too. Reorganizing also makes your data file grow less than rebuilding a huge index.

After defragmentation of your indexes, which should be done on a regular basis, the size might be reduced dramatically.

Of course, even the online index operations do have impact on your system as sooner or later there will be some locks on your table. I think the only way is: try it and monitor it.

Using another fill factor will of course make your table or index even larger. If it is the double by using 50 % fill factor, I don't know if it is exactly that and my experience using different fill factors is quite small...

The advantage of using a higher fill factor is that it MIGHT reduce index fragmentation as there might be less page splits. Another thing to think of is how the data is inserted: what is the clustered index and ist the data inserted sequentially on the key column(s)? If yes changing the fill factor might not have any impact at all. Another question: Are there updates on existing records? and so on...

My recommendation: try the index reorganize or online-rebuild command and check how it impacts your system performance and index size.