[gentoo-user] LVM filter question

[gentoo-user] LVM filter question

[Alex Schuster]

Hi there!

I am using LVM heavily, but I decided to not use it for some additional, 
smaller hard drives I use for backups and that I do not want to spin up 
every time I do LVM stuff, like pvscan, lvscan, vgchange. As all devices are 
scanned in this case, I edited the filter in /etc/lvm/lvm.conf:

    filter = [ "r|/dev/nbd.*|", "r|/dev/sdd|", "a/.*/" ]

This should reject /dev/sdd from scanning. But it doesn't, pvscan spins it 
up. Any idea why it is not being ignored?

	Wonko

Re: [gentoo-user] LVM filter question

[David W Noon]

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On Fri, 01 Jul 2011 22:05:12 +0200, Alex Schuster wrote about
[gentoo-user] LVM filter question:

[snip]
>     filter = [ "r|/dev/nbd.*|", "r|/dev/sdd|", "a/.*/" ]
> 
> This should reject /dev/sdd from scanning. But it doesn't, pvscan
> spins it up. Any idea why it is not being ignored?

The regular expression that precedes the one involving /dev/sdd
provides a clue: it would appear that LVM wraps the r.e. with ^ and $
so that it completes a string.

So, your r.e. should read:

   r|/dev/sdd.*|

which decodes to "reject ^/dev/sdd.*$ ".

This suppresses the scans of /dev/sdd1, /dev/sdd2, etc.

Now, you might not have any partitions on /dev/sdd, but LVM cannot
readily know that without reading the partition table, which spins up
the drive.  I guess LVM doesn't trust or, at least, depend upon udev
to supply the partition details.
-- 
Regards,

Dave  [RLU #314465]
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
dwnoon@ntlworld.com (David W Noon)
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*

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Re: [gentoo-user] LVM filter question

[Alex Schuster]

David W Noon writes:

> On Fri, 01 Jul 2011 22:05:12 +0200, Alex Schuster wrote about
> [gentoo-user] LVM filter question:
> 
> [snip]
> 
> >     filter = [ "r|/dev/nbd.*|", "r|/dev/sdd|", "a/.*/" ]
> > 
> > This should reject /dev/sdd from scanning. But it doesn't, pvscan
> > spins it up. Any idea why it is not being ignored?
> 
> The regular expression that precedes the one involving /dev/sdd
> provides a clue: it would appear that LVM wraps the r.e. with ^ and $
> so that it completes a string.
> 
> So, your r.e. should read:
> 
>    r|/dev/sdd.*|
> 
> which decodes to "reject ^/dev/sdd.*$ ".
> 
> This suppresses the scans of /dev/sdd1, /dev/sdd2, etc.
> 
> Now, you might not have any partitions on /dev/sdd, but LVM cannot
> readily know that without reading the partition table, which spins up
> the drive.  I guess LVM doesn't trust or, at least, depend upon udev
> to supply the partition details.

Good idea, didn't think about this. I tried that, but it did not help. 
/dev/sdd indeed has no partitions, the whole drive is a LUKS container.

Looks like this just does not work at all. Too bad. I have two big 1.5 TB 
drives, one as system drive, the other as identical backup drive. And then 
there are five more smaller drives for stuff I do not need regularly. Any 
LVM operation takes a while when all those drives have to spin up first.

Another annoying problem is KDE's / Dolphin's trash. When I delete something 
to the trash, all drives (or at least some, I have to investigate this 
further) that have mounted partitions spin up, one after another.

	Wonko

Re: [gentoo-user] LVM filter question

[David W Noon]

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On Sat, 02 Jul 2011 14:19:08 +0200, Alex Schuster wrote about "Re:
[gentoo-user] LVM filter question":

>David W Noon writes:
[snip]
>> So, your r.e. should read:
>> 
>>    r|/dev/sdd.*|
>> 
>> which decodes to "reject ^/dev/sdd.*$ ".
>> 
>> This suppresses the scans of /dev/sdd1, /dev/sdd2, etc.
>> 
>> Now, you might not have any partitions on /dev/sdd, but LVM cannot
>> readily know that without reading the partition table, which spins up
>> the drive.  I guess LVM doesn't trust or, at least, depend upon udev
>> to supply the partition details.
>
>Good idea, didn't think about this. I tried that, but it did not help. 
>/dev/sdd indeed has no partitions, the whole drive is a LUKS container.

My best suggestion is to create a maximal primary partition as /dev/sdd1
and use that as your LUKS volume.  That way, LVM will receive the
partition details from udev and *might* not bother re-reading the
partition table (but don't bet big bucks on it).
- -- 
Regards,

Dave  [RLU #314465]
======================================================================
dwnoon@ntlworld.com (David W Noon)
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Re: [gentoo-user] LVM filter question

[Alex Schuster]

David W Noon wrote:

> My best suggestion is to create a maximal primary partition as /dev/sdd1
> and use that as your LUKS volume.  That way, LVM will receive the
> partition details from udev and *might* not bother re-reading the
> partition table (but don't bet big bucks on it).

OK, I tried that now with an external drive that also spins down after some 
minutes - hdparm -Y does not work for external drives it seems. I made a 
single partition /dev/sdj1 (BTW, what will happen if I add 17 more drives? 
and I run out of letters?), waited until the drive spun down, issued pvscan 
and whooooooosh, the drive is back.

So it seems there is no solution, I think I just have to live with this. 
AFAIK spinning up and down often is not too bad for a drive nowadays, but 
some drives are 5 years old. 

All drives also spin up when I let Digikam retrieve photos from my camera. 
And it seems drives with mounted partitions also sometimes spin down then I 
delete files, but I cannot reproduce this right now. Strange. But this would 
be great, because it's annoying to let a drive spin up just because I delete 
a file somewhere.

Thanks for your ideas David, too bad it didn't work.

	Wonko