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

[Ben Huang]

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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