[linux-lvm] device-mapper may have read performance issue

[Eugene Vilensky]

Hi all,
How important are these read ahead settings for random, database IO?

On 10/10/08, Ben Huang <ben_devel at yahoo.cn> wrote:
> Hi all,
>
> --- Peter Keller <pkeller at globalphasing.com>写道:
>
>> Hi all,
>>
>> On Wed, 8 Oct 2008, thomas62186218 at aol.com wrote:
>>
>> > Ben,
>> >
>> > I have seen this same issue as well. I have
>> created an md device capable of
>> > 425MB/sec using the hdparm -t command, yet an LVM
>> volume fully comprising
>> > this md device only got about 150MB/sec. I am not
>> sure what the issue is. I
>> > am running Ubuntu Hardy 804 server edition,
>> 64-bit.
>> >
>> > -Thomas
>>
>> I have fixed this kind of problem by tweaking the
>> readahead of the LVM
>> volume using 'blockdev --setra' and/or 'blockdev
>> --setfra'.
>
> It make effect
>
>
> blockdev --setra 65536 /dev/md0
> blockdev --setra 65536 /dev/mapper/DG5-lv1
>
> dd if=/dev/md0 of=/dev/null bs=1M
> 353185562624 bytes (353 GB) copied, 420.033 s, 841
> MB/s
>
> dd if=/dev/mapper/DG5-lv1 of=/dev/null bs=1M
> 155551006720 bytes (156 GB) copied, 216.576 s, 718
> MB/s
>
> Warm regards,
> -Ben
>
>
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-- 
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Eugene Vilensky
evilensky at gmail.com