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Re: [linux-lvm] Setting readahead for Logical Volumes via udev

Hey Peter,

Thanks for the response. I've previously tried the "change" action, and adding the specifier for the DM_ACTIVATION environment variable had no effect. I'm also aware of the capability to set the readahead on a per-volume basis, but I'm looking for a solution which handles setting these values at boot time and/or volume creation time.


On Tue, May 20, 2014 at 2:03 AM, Peter Rajnoha <prajnoha redhat com> wrote:
On 05/19/2014 05:58 PM, David Wittman wrote:
> Hey all,
> I'm having an issue tuning the readahead value for my Logical Volumes
> via udev. In short, I'm trying to create a rule that sets the readahead
> attribute for each of my Logical Volumes at boot time or upon the
> creation of a new volume. udev seems like the perfect place to do this,
> but for some reason or another LVM seems to be overriding these settings.
> Here's the udev rule I'm using, followed by an example:
> ```
> # cat /etc/udev/rules.d/83-readahead.rules
> # Set the readahead on non-spinning disks to 8kb (16 512b sectors)
> ACTION="" KERNEL=="dm-*", ATTR{queue/rotational}=="0",
> ATTR{bdi/read_ahead_kb}="8"

Try ACTION="" KERNEL=="dm-*", ENV{DM_ACTIVATION}=="1", ATTR ....

Anyway, there's direct way to set the readahead value using LVM tools with:
  lvcreate/lvchange -r/--readahead (see man lvcreate and lvchange for more info).


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