Re: confused about raw-io blocksizes

[Andreas Dilger <adilger@turbolabs.com>]

On Nov 10, 2001  00:52 +0100, Terje Eggestad wrote:
> I'm curious as to what sets the smallest legal blocksize for raw-io, I
> get different values for different partitions on the same disk drive.
> 
> In all my tests I've used
> raw /dev/raw/raw2 <block speclial file>
> and to test block size:
> dd if=/dev/raw/raw2 of=/dev/null bs=N count=1
> where N is either 512, 1024, or 4096.
> (I've a RH7.1 with a dd that do propper buffer alignment)
> Failure is always "invalid argument" which singify either misaligned
> buffer or illegal read length.
> 
> What confuses me is that when raw2 is bound to /dev/hda bs=512 is ok.
> However when binding raw2 to the different partitions on /dev/hda, some
> are ok with 512, some will only accept 1024, and one required 4096.

It may be getting confused with the filesystem blocksize.  Check tune2fs -l
for those devices.

> When creating an lvm vg on one partition (/dev/hda6), and I've created
> two logical volumes on it, one was ok with 1024 and the other required
> 4096. When binding a raw to /dev/hda6 dd with bs=512 was ok.

LVM is broken in this regard, unless you have a recent patch (Linus'
kernel does not).  I sent him a patch to fix that, but it did not get in.

What kernel version/LVM do you have?  Are you using LVM on all of these
partitions, or only some?  Did you have filesystems on them? 

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/