graid3 - requirements or manpage wrong?

[Pawel Jakub Dawidek]

On Wed, Nov 24, 2004 at 10:54:07AM +0100, Eirik ?verby wrote:
+> to the best of my ability I have been investigating the 'real' 
+> requirements of a raid-3 array, and cannot see that the following text 
+> from graid3(8) cannot possibly be correct - and if it is, then the 
+> implementation must be wrong or incomplete (emphasis added):
+> 
+> label      Create a RAID3 device.  The last given component will contain
+>                parity data, all the rest - regular data.  ***Number of 
+> compo-
+>                nents has to be equal to 3, 5, 9, 17, etc. (2^n + 1).***
+> 
+> I might be wrong, but I cannot see how a raid-3 array should require 
+> (2^n + 1) drives - I am fairly certain I have seen raid-3 arrays 
+> consisting of four drives, for example. This is also what I had hoped to 
+> accomplish.

This requirement is because we want sectorsize to be power of 2
(UFS needs it).
In RAID3 we want to send every I/O request to all components at once,
that's why we need sector size to be N*512, where N is a power of 2 value
AND because graid3 uses one parity component we need N+1 providers.

-- 
Pawel Jakub Dawidek                       http://www.FreeBSD.org
pjd at FreeBSD.org                           http://garage.freebsd.pl
FreeBSD committer                         Am I Evil? Yes, I Am!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-stable/attachments/20041124/3f94b717/attachment.bin