No not controllers. This is buses on the controller. 4 bits for this
should be the lower limit. The smallest SSA that you can buy from SUN for
example has already 6 buses.
>
> : > unit 8 bits
>
> 256 devices per controller? SCSI??? Really? Wow!
Not exactly surprising. Just look in the SCSI-3 spec and at a whole lot of
available hardware. All the serial SCSI variants do support 8 bit device
IDs.
> : > LUN 8 bits
>
> 256 LUN's per SCSI ID? Gosh! 2.0.33 has 7 or 8 or 32 (depending on the
> driver).
Yes, that is indeed too high. There are 3 bit defined for this.
> : > partition 6 bits
>
> 64 partitions per disk? Yikes! Few commercial OS's have that many
> partitions per disk (Solaris allows 8), but OK... lets have 64 partitions.
Look at IDE......
> And Mike's comments...
>
> : And that is only for one controller. Now imagine having several of them.
> : A 12GB or even larger root partition would be real fun.
> Yup. Great sanity check. Let me help you into this long shirt which
> does up at the back...
Let me put it that way. A Sparc E4000 could have up to 40 controllers
which is another 6 bit.
> : I can already see the smile on the faces of the hard disc
> : manufacturers.....
>
> You sure made me smile.
>
> Now, 16 controllers, 16 units (wide SCSI), 32 LUNs, 64 partitions makes
> 4 bits + 4 bits + 5 bits + 6 bits = 19 bits
And now lets add everything up once again...
6 bit controllers + (at least) 4 bit SCSI buses (channels) per controller
+ 8 bit units + 3 bit LUNs + 6 bit partitions = 27 bits
YouŽd even need a bit or two more if you want to stay current with the
number of supported channels (buses) per controller.
Now calculate the amount of diskspace you will need for the inodes
and then tell me where you are going to store them.....
Mike