Howto create a new jffs2

[Krypton]

>> Creating 5 MTD partitions on "SA1100 flash":
>> 0x00000000-0x00020000 : "firmware"
>> 0x00020000-0x00040000 : "params"
>> 0x00040000-0x00140000 : "kernel"
>> 0x00140000-0x00fe0000 : "rootdisk"
>> 0x00fe0000-0x01000000 : "test"

> Try, mount -t jffs2 /dev/mtdblock4 <dir>

I already have tried this but unsuccesfully.
Error : "No such file or directory"

Other suggestions ?

Cheers