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Date:	Wed, 07 Mar 2012 23:36:39 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org,
	Lukas Czerner <lczerner@...hat.com>
Subject: Re: Some interesting input from a flash manufacturer

>>>>> "Ted" == Ted Ts'o <tytso@....edu> writes:

Ted> But min_io currently means the smallest size that we're allowed to
Ted> write, correct?  

Without incurring a penalty, yes. That was conceived in the standards
with 4K sectors and RAID RMW in mind. But I think it would apply to SSDs
as well. Depending on how mkfs.* interpret the field, obviously.


Ted> And the flash page size could be 128k and 512 byte writes might be
Ted> perfectly OK; it's just that writes are more optimal at 128k, and
Ted> would be even more optimal at the erbase block size of 4 megs.

Yep. Just like in the RAID case where the writing the full stripe chunk
is better than just a logical block. And a full stripe is even better.


Ted> That's why I'm not sure it makes sense to use the existing fields,
Ted> since it will confuse file system utilities that are reading those
Ted> fields.

Happy to add new fields if it makes sense. But right now ATA ACS doesn't
even have anything corresponding to the SCSI fields that populate min_io
and opt_io.

-- 
Martin K. Petersen	Oracle Linux Engineering
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