Subject: Re: UBC status
To: Matthew Jacob <>
From: Eduardo E. Horvath <>
List: tech-kern
Date: 09/28/1999 08:43:03
On Mon, 27 Sep 1999, Matthew Jacob wrote:

> On Mon, 27 Sep 1999, Thor Lancelot Simon wrote:
> > How can Solaris preserve FFS metadata consistency guarantees if it
> > writes using simple tags?
> > 
> Got me on that one. Eduardo?

Disk technology is an area where theory and reality diverge.  To a certain
extent it isn't really worth bothering with:

1) To my knowledge, ordered metadata writes have not been incorporated yet
so metadata is still written synchronously.

2) Cacheing is disabled on all disks, so when the I/O hits the disk it's

3) Current disks do no write verification, so the only way you are 
guaranteed that the metadata you just wrote out really is valid is to try
to read it back in.

4) RAID boxes with multipl paths and write-back caches complicate the
matter significantly.

Eduardo Horvath
	"I need to find a pithy new quote." -- me