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

[David Wittman]

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.

Dave


On Tue, May 20, 2014 at 2:03 AM, Peter Rajnoha <prajnoha at 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=="add", KERNEL=="dm-*", ATTR{queue/rotational}=="0",
> > ATTR{bdi/read_ahead_kb}="8"
> >
>
> Try ACTION=="change", 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).
>
> --
> Peter
>
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