Subject: RE: DEV_B_SIZE
To: 'Julian Elischer' <>
From: Jamey Kirby <>
List: tech-kern
Date: 01/31/2003 11:55:33
Who will do the translation?

Will there be a device driver that makes the 4K disk look like a 512
byte disk? If so, the device driver would have to pre-read the 4K,
modify the 512 byte section and re-write the entire 4K. This would kill

If this will be handled in the drive, the same sort of logic must be
employed and surly there will be a performance problem; unless the drive
will be able to write the 512 bytes without a pre-read.

How easy is it to change the firmware in the drive to make it a 4K block
drive? I would be willing to tinker with a 4K drive and provide some


-----Original Message-----
From: owner-freebsd-fs@FreeBSD.ORG [mailto:owner-freebsd-fs@FreeBSD.ORG]
On Behalf Of Julian Elischer
Sent: Friday, January 31, 2003 11:49 AM
To: Steve Byan
Cc: phk@FreeBSD.ORG; freebsd-fs@FreeBSD.ORG;
Subject: Re: DEV_B_SIZE 

One thign I thought of is that it is not uncommon to 'dd' an entire
filesystem from one partition to another.
If we create a filesystem that is 'aligned' and we copy it to be 
'unalligned', we'd have a sudden performance drop for no immediatly
obvious reason. What was one write, would become a 2-sector read,
modify and 2-sector write. Especially when copying from one failing
drive to another with slightly different characteristics.

The idea isn't bad but I think it should be sold as a 4k sector
drive, with small print saying it can handle 512byte IO
instead of the other way around.

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