Re: [dm-devel] Bug#648367: device-mapper devices such as dm-crypt always have rotational=1; should inherit "rotational" setting from underlying devices

[Milan Broz <mbroz redhat com>]

On 11/15/2011 05:41 PM, Josh Triplett wrote:
> I didn't know about that command; very nice, thanks!  lsblk confirms
> that on my system, the physical disk has rotational=0 but the dm-crypt
> and LVM devices have rotational=1:
> 
> NAME                   ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED
> sda                            0    512      0     512     512    0 cfq
> ├─sda1                         0    512      0     512     512    0 cfq
> └─sda2                         0    512      0     512     512    0 cfq
>   └─sda2_crypt (dm-0)          0    512      0     512     512    1 
>     ├─leaf-swap (dm-1)         0    512      0     512     512    1 
>     └─leaf-root (dm-2)         0    512      0     512     512    1 
> 
> Does that help?

Thanks.

As noted on that bug earlier, it is already fixed in 3.2-rc1
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=4693c9668fdcec229825b3763876b4744f9e6d5e

(I thought it is fixed long time ago!)

There is no problem in DM layer with this (dmcrypt does not have own io scheduler)
but perhaps FS can use this flag for some optimization tuning, dunno.

Milan