Date: Fri, 19 Mar 2010 12:44:37 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: Thiago Damas <tdamas@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: ATA 4K sector issues Message-ID: <86hboczgbe.fsf@ds4.des.no> In-Reply-To: <f8e3d83f1003181146o3366e9en9422f11e305475c8@mail.gmail.com> (Thiago Damas's message of "Thu, 18 Mar 2010 15:46:31 -0300") References: <alpine.BSF.2.00.1003171114280.74067@mignon.ki.iif.hu> <86tysf58a2.fsf@ds4.des.no> <alpine.BSF.2.00.1003171652260.74067@mignon.ki.iif.hu> <f8e3d83f1003171034m5e75eae4r5e8b31d88d361d3b@mail.gmail.com> <367b2c981003171112n785ea9d4q21d00b533819ca67@mail.gmail.com> <f8e3d83f1003171117k20d553b7y7ce4c3c8ed2f5c96@mail.gmail.com> <201003172023.o2HKNNbj069321@apollo.backplane.com> <201003172111.o2HLBIgJ069873@apollo.backplane.com> <f8e3d83f1003171417s60196803ra4884dae487edb9a@mail.gmail.com> <f8e3d83f1003181146o3366e9en9422f11e305475c8@mail.gmail.com>
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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
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