[linux-lvm] Strange behaviour with initramfs and read-ahead settings

[Michael Guntsche]

On 2009.11.28 15:31:47 , Milan Broz wrote:
> the logic is simple here
> - if readahead is set to auto, it should inherit value from underlying device
> for all LVs on that PV
> - if there is explicitly set value in metadata, it should always use that
> (you can switch back to auto by specifying -r auto)

I updated the initramfs and all binaries and configs are the same. While
debugging it further I noticed something. Since this is a server I
connect via SSH. Immediately after reboot as soon as the ssh daemon
started the read-ahead was ok (checked via blockdev). A few seconds
later the numbers changed. Looking through my init scripts I saw that
the mdadm --monitor daemon was started as well. I temporarily disabled
it and checked after a reboot. The numbers did not change. I re-enabled
the daemon but the numbers did not change either. I tried to reproduce
the problems several times now but did not succeed. Of course this could
be a red herring and the problem will re-appear but as it is now it
seems LVM is doing the right thing and something else is changing the RA
on my setup here. I debug this further the next time the problem shows
up.

Please mind, in all this tests I only updated the initramfs only once
and the problem was still there so I am ruling out a miss-configuration.
It looks more likely that the number is changed under special
circumstances.

Kind regards,
Michael