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Re: [linux-lvm] LVM2 seems to chop performance by 33%



Miguel Cabeça wrote:

Hi,

I didn't think lvm2 had such a big performance hit?

65Mb/s on the raid5 device
44Mb/s on the lv

Did you try to ajust the read ahead with blockdev on the LV itself?

# blockdev --setra XXXX /dev/sda  (raid5 device, just for comparisson)
# blockdev --setra XXXX /dev/vg/lv (lv)

Try some values for the readahead. On my system I use 2048.

No, I didn't hmm... man blockdev useful - new to me :) Not seen it on any googling to do with lvm.

I'll try this later when it's idle - thanks for the suggestion.

I do already have
 Read ahead sectors     100
in the lvdisplay

yet blockdev --getra /dev/video_vg/video_lv
reports 256 (and, to be sure --getss says 512byte sectors)

Why is this different?

David
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