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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Thiago Damas <tdamas@gmail.com>
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Date: Fri, 19 Mar 2010 12:44:37 +0100
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	(Thiago Damas's message of "Thu, 18 Mar 2010 15:46:31 -0300")
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Cc: freebsd-hackers@freebsd.org
Subject: Re: ATA 4K sector issues
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Thiago Damas <tdamas@gmail.com> writes:
> I tested now with 1Mb (2048 blocks) at the begining of disk, and same
> behaviour: slow write speed and high disk latency.

It just occurred to me - if I'm not mistaken, when the disk block size
is larger than either DFLTPHYS (64 kB), the kernel will do a
read-modify-write no matter how much data you write.  You should make
sure the filesystem never sees a block size larger than that (e.g. with
a four-disk stripe or a five-disk raid5, the individual disks' block
size should not exceed DFLTPHYS / 4, because the array's block size will
be 4 x the LCM of the individual disks' block sizes)

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no