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Date:	Wed, 12 Nov 2014 10:54:32 +0100
From:	Gionatan Danti <>
Subject: Re: AHCI maximum transfer size

On 16/09/2014 10:56, Gionatan Danti wrote:
>> Hi all,
>> I searched the list and the internet for this question, but I did not
>> find a definitive answer.
>> I wonder what is the maximum AHCI transfer size for kernel 2.6.32.x
>> Let me explain: using a command as "dd if=/dev/zero of=/dev/sda bs=2M" I
>> can see, via iostat, that request-size is at 2M (as expected). However
>> it seems to me that the effective transfer size is way lower: disabling
>> writeback cache on the target disk, I see very low performance even for
>> big-chunk transfers.
>> Googling, I found this post on stackoverflow stating that maximum
>> observerd AHCI transfer size (with a SATA protocol analyzer) is 128KB:
>> The stackoverflow post seems to agree with this old article:
>> Anyone has any idea of how to find (and eventually change) the used AHCI
>> transfer size without touching the code?
>> NOTE: please CC me directly.
>> Regards.
> Hi all,
> any idea on the subject?
> Regards.

Hi guys,
anyone with a suggestion?

Thank you.

Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. -
email: -
GPG public key ID: FF5F32A8
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