Subject: Re: DEV_B_SIZE
To: Julian Elischer <>
From: Terry Lambert <>
List: tech-kern
Date: 01/31/2003 16:44:07
Julian Elischer wrote:
> I presume that if such a drive were made, thre would be some way to
> identify it?
> It would be very easy to configure a filesystem to have a minimum
> writable unit size of 4k, and I assume that doing so would be
> slightly advantageous. (no Read/modify/write). it would however
> be good if we could easily identify when doing so was a good idea.

Substantial modifications would be required to the UFS directory
management code to support both old and new disks in the same
machine with the same FS code.

Assuming that was addressed by making the DEVBSIZE define into a
variable based on the underlying device, there's the problem of
device concatenation.  Your devices would have to be made up of
homogeneous components, too, so once you got them to coexist with
old disks, you would still not be able to get them to aggregate
with them, in, e.g., a RAID 0, and maybe not in any RAID set.

> I'd say that this means that the drive should hold the active 4k block
> in nvram or something..

This would be very useful, but unlikely in the extreme, I think,
because of the associated costs.  8-(.  But it would be very, very

-- Terry