Re: [gentoo-user] lvmetad Errors

[Alan McKinnon]

On 12/07/2015 22:46, Daniel Frey wrote:
> On 07/12/2015 12:25 PM, Alan McKinnon wrote:
>> It's because the "RAID" abilities built into most motherboards are
>> really shitty. Very little, if any, optimization going on, no real
>> intelligence, and the whole thing just looks and feels like it's no more
>> than 2 or more volumes shoved into one group. You would probably be
>> better off adding both disks to ove LVM VG and telling the system to do
>> simple striping or mirroring.
> 
> It can also be noticeable with a slower CPU, as all tasks are offloaded
> to the CPU. If you are doing I/O heavy tasks (like compiling) it can be
> very noticeable. Also beware Highpoint cards - quite a few of them are
> no better than onboard RAID - their prices reflect this.
> 
>> Proper hardware RAID using a proper RAID adapter is a whole different
>> story. Those tend to have proper firmware and control the disks
>> properly. They do the optimizations you expect, they will reorder writes
>> and do something sane with reads, and are worth the money is you need
>> RAID. However, most still only do a subset of desirable RAID, usually 0,
>> 1 and 5.
> 
> When I upgraded my mythtv backend with a 9750-8i (a real RAID card ~$800
> at the time I got it) the difference in I/O performance is staggering.
> Mine supports RAID 6 and 10 as well.

Over the years I've seen similar results from Adaptect cards too
(usually the models Dell ships)


> 
>> Linux software RAID, done in-kernel, is an amazing compromise. It's
>> almost as efficient as good hardware RAID, and covers all bases and RAID
>> types. Yes, it is somewhat more complex and you do have to use
>> management utilities when working with it. It's similarly complex to
>> administrating say LVM (not the same, just same order of magnitude) and
>> comes with the benefit of NOT costing half a server motherboard :-)
> 
> It also has the benefit of being able to recover a RAID on a separate
> machine. If your RAID HBA goes and you can't find a replacement, you're
> screwed.

That's the downside of hardware raid. Oftentimes, if the disks found
when the card boots are not it's own disks, or don't have the correct
magic number in the firmware, you can be royally screwed.

> 
> (Comments are from my first hand experience on my mythtv backend at
> home, I'd tried Highpoint, motherboard fakeraid, and mdadm before
> getting a real RAID HBA.)


-- 
Alan McKinnon
alan.mckin...@gmail.com

Re: [gentoo-user] lvmetad Errors

[Daniel Frey]

On 07/12/2015 12:25 PM, Alan McKinnon wrote:
> It's because the "RAID" abilities built into most motherboards are
> really shitty. Very little, if any, optimization going on, no real
> intelligence, and the whole thing just looks and feels like it's no more
> than 2 or more volumes shoved into one group. You would probably be
> better off adding both disks to ove LVM VG and telling the system to do
> simple striping or mirroring.

It can also be noticeable with a slower CPU, as all tasks are offloaded
to the CPU. If you are doing I/O heavy tasks (like compiling) it can be
very noticeable. Also beware Highpoint cards - quite a few of them are
no better than onboard RAID - their prices reflect this.

> Proper hardware RAID using a proper RAID adapter is a whole different
> story. Those tend to have proper firmware and control the disks
> properly. They do the optimizations you expect, they will reorder writes
> and do something sane with reads, and are worth the money is you need
> RAID. However, most still only do a subset of desirable RAID, usually 0,
> 1 and 5.

When I upgraded my mythtv backend with a 9750-8i (a real RAID card ~$800
at the time I got it) the difference in I/O performance is staggering.
Mine supports RAID 6 and 10 as well.

> Linux software RAID, done in-kernel, is an amazing compromise. It's
> almost as efficient as good hardware RAID, and covers all bases and RAID
> types. Yes, it is somewhat more complex and you do have to use
> management utilities when working with it. It's similarly complex to
> administrating say LVM (not the same, just same order of magnitude) and
> comes with the benefit of NOT costing half a server motherboard :-)

It also has the benefit of being able to recover a RAID on a separate
machine. If your RAID HBA goes and you can't find a replacement, you're
screwed.

(Comments are from my first hand experience on my mythtv backend at
home, I'd tried Highpoint, motherboard fakeraid, and mdadm before
getting a real RAID HBA.)

Dan

Re: [gentoo-user] lvmetad Errors

[Alan McKinnon]

On 12/07/2015 20:51, Alex Thorne wrote:
> I'm afraid I won't be testing it any time soon -- I don't have any
> drives to pair at the moment. As for your comments about dmraid being
> 'fake', I'm a little confused. From what you say it sounds like this is
> the hardware RAID that comes with many motherboards. Why is hardware
> RAID undesirable over software RAID? Presumably the mdraid software
> option has an associated performance hit? Is it just that opaque
> proprietary firmware can't be trusted with the important task of looking
> after our data?

It's because the "RAID" abilities built into most motherboards are
really shitty. Very little, if any, optimization going on, no real
intelligence, and the whole thing just looks and feels like it's no more
than 2 or more volumes shoved into one group. You would probably be
better off adding both disks to ove LVM VG and telling the system to do
simple striping or mirroring.

I always got the feeling that such RAID facilities were little more than
a way to get Windows users to have one big disk instead of two smaller
ones using the simplest eans possible.

Proper hardware RAID using a proper RAID adapter is a whole different
story. Those tend to have proper firmware and control the disks
properly. They do the optimizations you expect, they will reorder writes
and do something sane with reads, and are worth the money is you need
RAID. However, most still only do a subset of desirable RAID, usually 0,
1 and 5.

Linux software RAID, done in-kernel, is an amazing compromise. It's
almost as efficient as good hardware RAID, and covers all bases and RAID
types. Yes, it is somewhat more complex and you do have to use
management utilities when working with it. It's similarly complex to
administrating say LVM (not the same, just same order of magnitude) and
comes with the benefit of NOT costing half a server motherboard :-)


> 
> On 6 July 2015 at 16:01, Peter Humphrey  > wrote:
> 
> On Monday 06 July 2015 10:19:36 Alex Thorne wrote:
> > I guess I did mean mdraid, but would you mind explaining the difference
> > (I've never used raid so don't know much about this)? Is dmraid 
> deprecated
> > in favour of mdadm?
> 
> Dmraid is the fake RAID that's included on most motherboards these
> days; it's
> meant for use with Windows and is enabled (or not) in the BIOS.
> There are
> Linux drivers, but we're always advised to use mdraid instead.
> Mdraid is all
> in software spread over the kernel, udev and user space*; it's not
> influenced
> at all by Windows as far as I know. Mdadm is the user-space
> administration
> program that comes with mdraid.
> 
> Mdadm creates /dev/mdX from one or more /dev/sdX or similar - e.g.
> my /dev/md1
> is built on /dev/sd[ab]1; /dev/md5 is on /dev/sd[ab]5 and /dev/md7 is on
> /dev/sd[ab]7. That last one also has LVM on it with a dozen or more
> logical
> volumes for segments of my overall file system.
> 
> If you want to play with mdraid, the old Gentoo guide is succinct
> but useful:
> 
> http://wwwold.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml
> 
> Well, it was, but suddenly it isn't there - even Google's search
> results end
> up in an empty page.
> 
> Ah, I've found the new version at https://wiki.gentoo.org/wiki/LVM .
> It must
> be very new - would you like to test it?  :-)
> 
> *  Yes, I know that udev runs in user space (="User Device"
> management) but I
> thought it was worth mentioning separately.
> 
> --
> Rgds
> Peter
> 
> 
> 


-- 
Alan McKinnon
alan.mckin...@gmail.com

Re: [gentoo-user] lvmetad Errors

[Alex Thorne]

I'm afraid I won't be testing it any time soon -- I don't have any drives
to pair at the moment. As for your comments about dmraid being 'fake', I'm
a little confused. From what you say it sounds like this is the hardware
RAID that comes with many motherboards. Why is hardware RAID undesirable
over software RAID? Presumably the mdraid software option has an associated
performance hit? Is it just that opaque proprietary firmware can't be
trusted with the important task of looking after our data?

On 6 July 2015 at 16:01, Peter Humphrey  wrote:

> On Monday 06 July 2015 10:19:36 Alex Thorne wrote:
> > I guess I did mean mdraid, but would you mind explaining the difference
> > (I've never used raid so don't know much about this)? Is dmraid
> deprecated
> > in favour of mdadm?
>
> Dmraid is the fake RAID that's included on most motherboards these days;
> it's
> meant for use with Windows and is enabled (or not) in the BIOS. There are
> Linux drivers, but we're always advised to use mdraid instead. Mdraid is
> all
> in software spread over the kernel, udev and user space*; it's not
> influenced
> at all by Windows as far as I know. Mdadm is the user-space administration
> program that comes with mdraid.
>
> Mdadm creates /dev/mdX from one or more /dev/sdX or similar - e.g. my
> /dev/md1
> is built on /dev/sd[ab]1; /dev/md5 is on /dev/sd[ab]5 and /dev/md7 is on
> /dev/sd[ab]7. That last one also has LVM on it with a dozen or more logical
> volumes for segments of my overall file system.
>
> If you want to play with mdraid, the old Gentoo guide is succinct but
> useful:
>
> http://wwwold.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml
>
> Well, it was, but suddenly it isn't there - even Google's search results
> end
> up in an empty page.
>
> Ah, I've found the new version at https://wiki.gentoo.org/wiki/LVM . It
> must
> be very new - would you like to test it?  :-)
>
> *  Yes, I know that udev runs in user space (="User Device" management)
> but I
> thought it was worth mentioning separately.
>
> --
> Rgds
> Peter
>
>
>

Re: [gentoo-user] lvmetad Errors

[Peter Humphrey]

On Monday 06 July 2015 10:19:36 Alex Thorne wrote:
> I guess I did mean mdraid, but would you mind explaining the difference
> (I've never used raid so don't know much about this)? Is dmraid deprecated
> in favour of mdadm?

Dmraid is the fake RAID that's included on most motherboards these days; it's 
meant for use with Windows and is enabled (or not) in the BIOS. There are 
Linux drivers, but we're always advised to use mdraid instead. Mdraid is all 
in software spread over the kernel, udev and user space*; it's not influenced 
at all by Windows as far as I know. Mdadm is the user-space administration 
program that comes with mdraid.

Mdadm creates /dev/mdX from one or more /dev/sdX or similar - e.g. my /dev/md1 
is built on /dev/sd[ab]1; /dev/md5 is on /dev/sd[ab]5 and /dev/md7 is on 
/dev/sd[ab]7. That last one also has LVM on it with a dozen or more logical 
volumes for segments of my overall file system.

If you want to play with mdraid, the old Gentoo guide is succinct but useful:

http://wwwold.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml

Well, it was, but suddenly it isn't there - even Google's search results end 
up in an empty page.

Ah, I've found the new version at https://wiki.gentoo.org/wiki/LVM . It must 
be very new - would you like to test it?  :-)

*  Yes, I know that udev runs in user space (="User Device" management) but I 
thought it was worth mentioning separately.

-- 
Rgds
Peter

Re: [gentoo-user] lvmetad Errors

[Alex Thorne]

I guess I did mean mdraid, but would you mind explaining the difference
(I've never used raid so don't know much about this)? Is dmraid deprecated
in favour of mdadm?

Yes, I think most Gentoo installs I've done have had some small
warnings/error messages somewhere which I've never quite managed to
eliminate...

On 6 July 2015 at 08:54, Peter Humphrey  wrote:

> On Sunday 05 July 2015 18:01:37 Alex Thorne wrote:
> > Unfortunately dmraid is not in any runlevel. I think it is lvm that's
> > starting lvmetad despite use_lvmetad=0 being set in the configuration
> file.
> > Unfortunately I think I'm just going to have to learn to live with the
> > error message.
>
> I hope you meant "mdraid".
>
> I've rebuilt my system recently (to go back from ~amd64 to amd64) and now I
> can't find a combination that avoids all error messages, so I seem to be
> in the
> same boat as you now  :0
>
> --
> Rgds
> Peter
>
>
>

Re: [gentoo-user] lvmetad Errors

[Peter Humphrey]

On Sunday 05 July 2015 18:01:37 Alex Thorne wrote:
> Unfortunately dmraid is not in any runlevel. I think it is lvm that's
> starting lvmetad despite use_lvmetad=0 being set in the configuration file.
> Unfortunately I think I'm just going to have to learn to live with the
> error message.

I hope you meant "mdraid".

I've rebuilt my system recently (to go back from ~amd64 to amd64) and now I 
can't find a combination that avoids all error messages, so I seem to be in the 
same boat as you now  :0

-- 
Rgds
Peter

Re: [gentoo-user] lvmetad Errors

[Alex Thorne]

Unfortunately dmraid is not in any runlevel. I think it is lvm that's
starting lvmetad despite use_lvmetad=0 being set in the configuration file.
Unfortunately I think I'm just going to have to learn to live with the
error message.

Thanks,
Alex

On 25 June 2015 at 10:19, Peter Humphrey  wrote:

> On Wednesday 24 Jun 2015 12:13:06 Alex Thorne wrote:
>
> > I used to get the following error in /var/log/rc.log
> > /run/lvm/lvmetad.socket: connect failed: No such file or directory
> > I am not sure why this was happening, but I read that one fix was to
> > disable lvmetad entirely. And so I set
> >use_lvmetad = 0
> > in /etc/lvm/lvm.conf.
> >
> > However, now I get error messages of the following form (e.g. when
> running
> > grub2-mkconfig):
> >   WARNING: lvmetad is runing but disabled. Restart lvmetad before
> enabling
> > it!
>
> I don't have an rc.log but I used to see this scroll by during boot and
> shutdown. The cure seems to be to remove mdraid from the boot run-level
> [1].
>
> I don't properly understand what's going on here: I needed mdraid in boot
> while building the system, but once it was up and running and udev was
> starting the RAID volumes it was better to remove it. I still have
> use_lvmetad
> = 1. Bug 521280 refers.
>
> > I ran
> >/etc/init.d/lvmetad needsme
> > and got
> >lvm-monitor lvm
> > I don't understand why lvm is starting lvmetad even when I have disabled
> > it. lvmetad is certainly not in any runlevel itself and I just don't know
> > where to go from here.
> >
> > I would appreciate some advice on how to fix either problem (the socket
> > connect issue when lvmetad is enabled, or the fact that lvmetad still
> > starts when it's disabled...)
>
> [1] ...and have a rescue system ready to chroot from and put it back
> :-)
>
> --
> Rgds
> Peter
>
>
>

Re: [gentoo-user] lvmetad Errors

[Peter Humphrey]

On Wednesday 24 Jun 2015 12:13:06 Alex Thorne wrote:

> I used to get the following error in /var/log/rc.log
> /run/lvm/lvmetad.socket: connect failed: No such file or directory
> I am not sure why this was happening, but I read that one fix was to
> disable lvmetad entirely. And so I set
>use_lvmetad = 0
> in /etc/lvm/lvm.conf.
> 
> However, now I get error messages of the following form (e.g. when running
> grub2-mkconfig):
>   WARNING: lvmetad is runing but disabled. Restart lvmetad before enabling
> it!

I don't have an rc.log but I used to see this scroll by during boot and 
shutdown. The cure seems to be to remove mdraid from the boot run-level [1].

I don't properly understand what's going on here: I needed mdraid in boot 
while building the system, but once it was up and running and udev was 
starting the RAID volumes it was better to remove it. I still have use_lvmetad 
= 1. Bug 521280 refers.

> I ran
>/etc/init.d/lvmetad needsme
> and got
>lvm-monitor lvm
> I don't understand why lvm is starting lvmetad even when I have disabled
> it. lvmetad is certainly not in any runlevel itself and I just don't know
> where to go from here.
> 
> I would appreciate some advice on how to fix either problem (the socket
> connect issue when lvmetad is enabled, or the fact that lvmetad still
> starts when it's disabled...)

[1] ...and have a rescue system ready to chroot from and put it back :-)

-- 
Rgds
Peter

[gentoo-user] lvmetad Errors

[Alex Thorne]

I have been getting some lvmetad related errors, some of which can
certainly be found on Google, but I haven't had luck fixing them so far.

I used to get the following error in /var/log/rc.log
/run/lvm/lvmetad.socket: connect failed: No such file or directory
I am not sure why this was happening, but I read that one fix was to
disable lvmetad entirely. And so I set
   use_lvmetad = 0
in /etc/lvm/lvm.conf.

However, now I get error messages of the following form (e.g. when running
grub2-mkconfig):
  WARNING: lvmetad is runing but disabled. Restart lvmetad before enabling
it!

I ran
   /etc/init.d/lvmetad needsme
and got
   lvm-monitor lvm
I don't understand why lvm is starting lvmetad even when I have disabled
it. lvmetad is certainly not in any runlevel itself and I just don't know
where to go from here.

I would appreciate some advice on how to fix either problem (the socket
connect issue when lvmetad is enabled, or the fact that lvmetad still
starts when it's disabled...)

Thanks,
Alex