Re: LVM on two disks - spin down?
Hi
On Thu, Oct 30, 2014 at 08:15:47PM +0100, b-misc@gmx.ch wrote:
> Hi all,
>
> If I have a LVM which uses two partitions on two different disks and at least
> one of its subvolumes is always in use, can the second disk spin
> down?
Depends on where that subvolume is mapped to.
It will probably be instructive if you run e.g.:
# pvdisplay --maps /dev/sda1
which will give the answer to "Which LVs occupy chunks of
/dev/sda1?". Or
# lvdisplay --maps /dev/vgname/lvname
which will give the answer to "Where is vgname/lvname actually
stored?"
(alternatively, run "vgcfgbackup vgname" and peruse /etc/lvm/backup/vgname)
>
> An example showing what I mean:
> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
> |/dev/sda1 | |/dev/sdb1 |
> |_ _ _ _ _ _ _ _| |_ _ _ _ _ _ _ _|
>
>
> lvmGrp = /dev/sda1 + /dev/sdb1
> _ _ _ _ _ _ _ _ _ _ _ _ _
> |lvm1 | |lvm2 | |lvm3 |
> |_ _ _ _| |_ _ _| |_ _ _ _ _ _|
>
> So since sdb is new, if I add lvm3 it will be on sdb1 and not sda1,
> correct?;
Assuming that /dev/sda1 is full, yes. Even so, you can force the
issue when creating the LV. Or by moving it afterwards.
> if I don't mount lvm3 automatically, can sdb spin down although lvm1 and lvm2
> are used?
I haven't actually tried that, but I believe so. As long as none of
the LVs which reside (even partially) on /dev/sdb1 are in use, yes.
Note that most LVM operations (lvcreate, pvdisplay etc) will wake up
*all* of the PVs.
> The reason for this setup is the possibility to extend e.g. lvm2 later with
> space on sdb1 if it is really required without any re-formatting. (Of course I
> will loose the spin down then, but for the time being I'd take care of my new
> disk.)
Remember that you can move portions of LVs around to suit you if you
like (without downtime) - courtesy of the (somewhat misnamed) pvmove
command. So even if you start off with the "wrong" layout, it's
relatively easy to fix.
Hope this helps
--
Karl E. Jorgensen
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