[linux-lvm] lvchange -r 256 lv-name does not work

[linux-lvm] lvchange -r 256 lv-name does not work

[Sachin Sant]

Hi , i came across a problem with lvchange command.

I have a VG with 3 pv and a lv created using command 

lvcreate -i3 -I32 -l98 -nmy_lv my_vg
lvdisplay shows 1024 as the value for Read Ahead Sectors.

When i use the command lvchange to change the value of read ahead
sector with value more that or equal to 256 i get following error..

linux# lvchange -r 340 /dev/my_vg/my_lv
lvchange -- ERROR "Invalid Argument" read ahead sector change
linux#
linux#

Is there a limitation that read ahead value cannot be greater 
than 255?

Thanks
-Sachin

[linux-lvm] lvchange -r 256 lv-name does not work

[Sachin Sant]

Hi , i came across a problem with lvchange command.

I have a VG with 3 pv and a lv created using command 

lvcreate -i3 -I32 -l98 -nmy_lv my_vg
lvdisplay shows 1024 as the value for Read Ahead Sectors.

When i use the command lvchange to change the value of read ahead
sector with value more that or equal to 256 i get following error..

linux# lvchange -r 340 /dev/my_vg/my_lv
lvchange -- ERROR "Invalid Argument" read ahead sector change
linux#
linux#

After debugging i found that in drivers/block/blkpg.c file blk_ioctl( )

Case BLKRASET :

	if (arg > 0xff )
		return -EINVAL;

Effectively this does not allow value greater that 255 for read ahead.
Is there a limitation that the read ahead sectors can't have value more
than 255 ? If yes then why lvdisplay shows 1024 as the default value for
read ahead sectors.

Thanks
-Sachin