[linux-lvm] Strange behaviour with initramfs and read-ahead settings
Michael Guntsche
mike at it-loops.com
Sat Nov 28 10:52:53 UTC 2009
Hi list,
I am currently running the 2.6.32-rc8 kernel with lvm2 version 2.02.54-1
on debian unstable.
Since my root is on LVM as well I use an initramfs for booting. The
setup I have consists of 5 disks in a RAID-5 with one PV on top of it.
Now for my problem. The md device correctly sets the read-ahead to 4096.
If I understand correctly lvm should get this value and set the
read-ahead on the LVs accordingly. This is not working correctly for
all my LVs.
Apart from the FIRST LV on the disk all the others show
Read ahead sectors auto
- currently set to 256
Since this did not seem to work I changed the RA with lvchange -r 4096
and rebooted. Swap now showed
Read ahead sectors 4096
while the other LVs still showed
Read ahead sectors 4096
- currently set to 256
lvs -o lv_read_ahead after boot
Rahead
2.00m
2.00m
2.00m
2.00m
2.00m
blockdev --getra showed 256 for each LV apart from the first one.
For testing purposes I took one LV (home) offline and back online again
lvchange -an;lvchange -ay
After that the readahead was set correctly to 4096. I am not sure what's
happening here. I would understand a problem with getting the values
automatically but right now they are saved in the metadata but are still
set to 256.
I am glad for any help on this topic, in the mean-time I am using
blockdev --setra to work around this problem.
Kind regards,
Michael Guntsche
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