Re: [PATCH][RFC]ext4 on 4k-sector drives without read-modify-write support

[James Bottomley <James.Bottomley@suse.de>]

On Mon, 2011-02-28 at 16:05 -0500, Ted Ts'o wrote:
> On Mon, Feb 28, 2011 at 03:19:21PM -0500, Martin K. Petersen wrote:
> > Kind of, yes. But that involves teaching every ATA driver in $LEGACY_OS
> > about 4KB logical blocks. There is little value is switching to 4KB
> > logical blocks in the first place. So the claim is that it is easier to
> > stick with 512-byte addressing, leave the I/O stack intact, and require
> > the filesystem to always issue aligned units of 4KB.
> > 
> > That saves the drive vendors from implementing RMW logic and puts the
> > burden on us. Perfect deal.
> 
> So it there a reliable way to detect that disk drives that don't have
> the Read-Modify-Write logic?  If that can be reflected up the I/O
> layer I can have mke2fs enforce that restriction, which currently we
> only enforce if the logical blocksize is 4k.

Well, we could blacklist it to force the logical block size up to 4k
based on identification by the inquiry strings (that, of course,
involves finding all the inquiry strings).  It's just that we're
practically out of blacklist bits ... it's just I thought we'd finally
got all manufacturers on the same page as standards compliance ... doing
something like this would send us back to the dark ages again.

Could we just have a campaign to send drives that fail like this back?
That might actually get the message across to the manufacturers .. and
it could arguably be covered under the warranty.

James