[linux-lvm] enclosure separation/turnoff

[linux-lvm] enclosure separation/turnoff

[Alexy Khrabrov]

I would like to see what would be a good way to use LVM
with a bunch of external SCSI enclosures ("boxes").  I have
several of these, with the number of drives ranging
from 1 to 2 to 4 per each.  First I created a logical volume
per each box, but then realized the sizes were not exactly
matched, and now I get thrashing when trying to move stuff
from one enclosure box to another.  So the first question
is, (1) how does one create a logical volume exactly corresponding 
to an external box (a set of drives)? (2) Is it a good idea
to stripe an external box, given that data moves occur primarily
between the boxes, not within each?  Then I'd stripe each
box with the number of stripes being the number of drives in it.
(3) Is there a way to resize the logical volumes so they are 
remapped to their enclosures exactly, without reloading the
contents?  (4) To make sure my latest box is done right, I created
a new volume group for it.  Is this a good use for multiple
volume groups (other than the usual lone "system")?

Now, I wanted to temporarily turn off the external enclosures
as I didn't need their contents.  However, Linux would not boot
properly!  Even when I disable the boxes in /etc/fstab,
it fails to boot; even when I deactivate the logical volumes
corresponding to the boxes with lvchange -a n <path>
for each, and deactivate the last box with vgchange -a n <group>,
failure on boot -- can't find many standard paths!  Looks
like vgscan thinks something is still there and I get a message
"spinning sdd", while sdd is in one of the deactivated LVs,
and I'm forced to power on all of the boxes even while none
is mounted nor used.  (5) How do I achieve clean separation so
that I can shut down any or all external enclosures easily?

Cheers,
Alexy Khrabrov

Re: [linux-lvm] enclosure separation/turnoff

[Patrick Caulfield]

On Tue, Feb 11, 2003 at 05:51:23PM -0500, Alexy Khrabrov wrote:
> 
> I would like to see what would be a good way to use LVM
> with a bunch of external SCSI enclosures ("boxes").  I have
> several of these, with the number of drives ranging
> from 1 to 2 to 4 per each.  First I created a logical volume
> per each box, but then realized the sizes were not exactly
> matched, and now I get thrashing when trying to move stuff
> from one enclosure box to another.  So the first question
> is, (1) how does one create a logical volume exactly corresponding 
> to an external box (a set of drives)? (2) Is it a good idea
> to stripe an external box, given that data moves occur primarily
> between the boxes, not within each?  Then I'd stripe each
> box with the number of stripes being the number of drives in it.
> (3) Is there a way to resize the logical volumes so they are 
> remapped to their enclosures exactly, without reloading the
> contents?  (4) To make sure my latest box is done right, I created
> a new volume group for it.  Is this a good use for multiple
> volume groups (other than the usual lone "system")?
> 
> Now, I wanted to temporarily turn off the external enclosures
> as I didn't need their contents.  However, Linux would not boot
> properly!  Even when I disable the boxes in /etc/fstab,
> it fails to boot; even when I deactivate the logical volumes
> corresponding to the boxes with lvchange -a n <path>
> for each, and deactivate the last box with vgchange -a n <group>,
> failure on boot -- can't find many standard paths!  Looks
> like vgscan thinks something is still there and I get a message
> "spinning sdd", while sdd is in one of the deactivated LVs,
> and I'm forced to power on all of the boxes even while none
> is mounted nor used.  (5) How do I achieve clean separation so
> that I can shut down any or all external enclosures easily?

It sounds like you really just want to use each disk with a single
partition on it. LVM in this instance is not going to buy you anything.

-- 

patrick

Re: [linux-lvm] enclosure separation/turnoff

[Alexy Khrabrov]

Well, I want to use LVM within each enclosure
to aggregate drives.  The problem is, when I don't
need a particular enclosure, I want to be able to power
it down and boot my server without that box altogether,
but I'm forced to power it on even if the LV is not
mounted in /etc/fstab!  And even if it's deactivated
with lvchange -a n!  It seems to me that the underlying
PVs for that LV are being spinned on boot despite all
of the above, is that right?  Do I have to go deactivate
each PV then?...

Cheers,
Alexy

Re: [linux-lvm] enclosure separation/turnoff

[Patrick Caulfield]

On Wed, Feb 12, 2003 at 11:33:41AM -0500, Alexy Khrabrov wrote:
> 
> Well, I want to use LVM within each enclosure
> to aggregate drives.  The problem is, when I don't
> need a particular enclosure, I want to be able to power
> it down and boot my server without that box altogether,
> but I'm forced to power it on even if the LV is not
> mounted in /etc/fstab!  And even if it's deactivated
> with lvchange -a n!  It seems to me that the underlying
> PVs for that LV are being spinned on boot despite all
> of the above, is that right?  Do I have to go deactivate
> each PV then?...

It should work fine if you make sure that one VG is mapped onto
the disks in one box only. Then LVM will only find the VGs that 
are available.
-- 

patrick