linux-kernel - Re: O_DIRECT to md raid 6 is slow

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Date:	Tue, 14 Aug 2012 18:12:24 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	kedacomkernel <kedacomkernel@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-raid <linux-raid@...r.kernel.org>
Subject: Re: O_DIRECT to md raid 6 is slow

Ubuntu's 3.2.0-27-generic.  I can test on a newer kernel tomorrow.

--Andy

On Tue, Aug 14, 2012 at 6:07 PM, kedacomkernel <kedacomkernel@...il.com> wrote:
> On 2012-08-15 08:49 Andy Lutomirski <luto@...capital.net> Wrote:
>>If I do:
>># dd if=/dev/zero of=/dev/md0p1 bs=8M
>>then iostat -m 5 says:
>>
>>avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>>           0.00    0.00   26.88   35.27    0.00   37.85
>>
>>Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
>>sdb             265.20         1.16        54.79          5        273
>>sdc             266.20         1.47        54.73          7        273
>>sdd             264.20         1.38        54.54          6        272
>>sdf             286.00         1.84        54.74          9        273
>>sde             266.60         1.04        54.75          5        273
>>sdg             265.00         1.02        54.74          5        273
>>md0           55808.00         0.00       218.00          0       1090
>>
>>If I do:
>># dd if=/dev/zero of=/dev/md0p1 bs=8M oflag=direct
>>then iostat -m 5 says:
>>avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>>           0.00    0.00   11.70   12.94    0.00   75.36
>>
>>Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
>>sdb             831.00         8.58        30.42         42        152
>>sdc             832.80         8.05        29.99         40        149
>>sdd             832.00         9.10        29.78         45        148
>>sdf             838.40         9.11        29.72         45        148
>>sde             828.80         7.91        29.79         39        148
>>sdg             850.80         8.00        30.18         40        150
>>md0            1012.60         0.00       101.27          0        506
>>
>>It looks like md isn't recognizing that I'm writing whole stripes when
>>I'm in O_DIRECT mode.
>>
> kernel version?
>
>>--Andy
>>
>>--
>>Andy Lutomirski
>>AMA Capital Management, LLC
>>--
>>To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>>the body of a message to majordomo@...r.kernel.org
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-- 
Andy Lutomirski
AMA Capital Management, LLC
--
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