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Date:      Fri, 31 Jan 2003 20:23:52 +0100
From:      phk@freebsd.org
To:        Steve Byan <stephen_byan@maxtor.com>
Cc:        freebsd-fs@freebsd.org, tech-kern@netbsd.org
Subject:   Re: DEV_B_SIZE 
Message-ID:  <25200.1044041032@critter.freebsd.dk>
In-Reply-To: Your message of "Fri, 31 Jan 2003 14:06:11 EST." <1010FEB6-354F-11D7-B26B-00306548867E@maxtor.com> 

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In message <1010FEB6-354F-11D7-B26B-00306548867E@maxtor.com>, Steve Byan writes
:

>> Not broken any worse than because of write-caching.
>
>Agreed, but IDEMA is proposing to do this to SCSI drives, too.

We've seen broken caching on SCSI as well, but not recently I think :-)

>But if someone were to plug a new 4K-block disk into a system compiled 
>to use 512 byte block disks, and the SCSI interface were faked to make 
>it appear that the disk could read and write 512-byte blocks, then what 
>happens? IDEMA's notion is that faking 512-byte logical size is good 
>enough to get new disks to work in systems running legacy code. My fear 
>is that it is not so simple.

If plug a 4k sector disk into a system which doesn't know how to find
out that the drive really is 4k sectors, then you will increase the
window for lossage.

>> The thing we really need is working tagged-queing...
>
>Since I believe tagged-queuing works in SCSI, I assume you are asking 
>for it in ATA? Or is there some feature missing from SCSI 
>tagged-queuing that you'd like to see?

Yes, I was talking ATA there.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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