[linux-lvm] LVM with multi-path disks?

[linux-lvm] LVM with multi-path disks?

[John DeFranco]

Hi,

Does LVM work with multi-path disks? For example I have
a fibre channel configuration in which I have two paths
to each disk. I pvcreate a disk and am able to use it
within a vg but when I reboot and do a vgscan, lvm cannot
find any vg's. If I remove the second path lvm can see
the vg fine.

Are there some configuration settings or such that need
to be enabled?

THanks.
-- 
==========

John DeFranco <defranco@cup.hp.com>
Software Engineer
Hewlett Packard, Cupertino
(408) 447-7543

Re: [linux-lvm] LVM with multi-path disks?

[Luca Berra]

On Fri, Aug 03, 2001 at 04:16:20PM -0700, John DeFranco wrote:
> Does LVM work with multi-path disks? For example I have
> a fibre channel configuration in which I have two paths
> to each disk. I pvcreate a disk and am able to use it
> within a vg but when I reboot and do a vgscan, lvm cannot
> find any vg's. If I remove the second path lvm can see
> the vg fine.

John, there is an addition for multi-path to the md driver
you can fetch it from the redhat source kernel rpm.
you can then stack lvm on top of md to achieve your goal

Regards,
Luca

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
 / \

Re: [linux-lvm] LVM with multi-path disks?

[Ragnar Kjørstad]

On Sat, Aug 04, 2001 at 05:40:49PM +0200, Luca Berra wrote:
> On Fri, Aug 03, 2001 at 04:16:20PM -0700, John DeFranco wrote:
> > Does LVM work with multi-path disks? For example I have
> > a fibre channel configuration in which I have two paths
> > to each disk. I pvcreate a disk and am able to use it
> > within a vg but when I reboot and do a vgscan, lvm cannot
> > find any vg's. If I remove the second path lvm can see
> > the vg fine.
> 
> John, there is an addition for multi-path to the md driver
> you can fetch it from the redhat source kernel rpm.
> you can then stack lvm on top of md to achieve your goal

E.g. you have a md0 device consisting of sda and sdb - would not lvm
find three different paths to the same data (sda, sdb, md0) when
scanning for physical volumes? Will that not cause problems?

From John's description it looks like vgscan can't handle multiple path
- and that's the problem - not that it is not able to take advantage of
it (loadbalance / failover).


-- 
Ragnar Kjorstad
Big Storage

Re: [linux-lvm] LVM with multi-path disks?

[Luca Berra]

On Sun, Aug 05, 2001 at 02:28:01AM +0200, Ragnar Kj�rstad wrote:
> On Sat, Aug 04, 2001 at 05:40:49PM +0200, Luca Berra wrote:
> > John, there is an addition for multi-path to the md driver
> > you can fetch it from the redhat source kernel rpm.
> > you can then stack lvm on top of md to achieve your goal
> 
> E.g. you have a md0 device consisting of sda and sdb - would not lvm
> find three different paths to the same data (sda, sdb, md0) when
> scanning for physical volumes? Will that not cause problems?

there is an (*horrible*) piece of code in pv_read_all_pv.c
that deals with multiple entries for the same PV, so all duplicate
PV are skipped, so the md will be the obly one detected.
what probably happened to John is, that his PV was killed by
this routine (they were duplicate and not md devices)

regards
L.
-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
 / \

Re: [linux-lvm] LVM with multi-path disks?

[Mark Glines]

On Sun, Aug 05, 2001 at 09:12:01AM +0200, Luca Berra wrote:
> On Sun, Aug 05, 2001 at 02:28:01AM +0200, Ragnar Kj?rstad wrote:
> > On Sat, Aug 04, 2001 at 05:40:49PM +0200, Luca Berra wrote:
> > > John, there is an addition for multi-path to the md driver
> > > you can fetch it from the redhat source kernel rpm.
> > > you can then stack lvm on top of md to achieve your goal
> > 
> > E.g. you have a md0 device consisting of sda and sdb - would not lvm
> > find three different paths to the same data (sda, sdb, md0) when
> > scanning for physical volumes? Will that not cause problems?
> 
> there is an (*horrible*) piece of code in pv_read_all_pv.c
> that deals with multiple entries for the same PV, so all duplicate
> PV are skipped, so the md will be the obly one detected.
> what probably happened to John is, that his PV was killed by
> this routine (they were duplicate and not md devices)

I would only think this is a problem when md isn't being used.  In the
above described situation, vgscan would see 2 devices which have md
headers (and ignore them), and one LVM signature (and use it)?

If the code does what you say, and LVM was using the dual-path SCSI
device directly, then it would detect one and ignore the other, and it
would still work as if there was only one route to the drive.

However, in this case, md is in the middle, and its md's job to handle
multi-path.  LVM should be ignoring md's lowlevel volumes anyway, and
act solely on the virtual device md exports.  Am I missing something?
-- 
#!/usr/bin/perl
while($_=shift){if($d==1){$a="$a \"$_\""}else{if(/^-(.+)/){$t
=$1;$i.=$t;if($i=~/-/){$i=~s/-//;$r=shift;$d=1}}else{$r=$_;$d
=1}}}die"Usage: $0 [-ix] [--] regex [paths]\n"if!$r;eval"\$r=
qr/$r/$i";$a='.'if!$a;@F=`find $a -type f`;chomp@F;for $f(@F)
{open(I,$f)or next;while(<I>){print"$f:$.:$_"if/$r/}close(I)}

Re: [linux-lvm] LVM with multi-path disks?

[Luca Berra]

On Sun, Aug 05, 2001 at 12:32:57AM -0700, Mark Glines wrote:
> On Sun, Aug 05, 2001 at 09:12:01AM +0200, Luca Berra wrote:
> > there is an (*horrible*) piece of code in pv_read_all_pv.c
> > that deals with multiple entries for the same PV, so all duplicate
> > PV are skipped, so the md will be the obly one detected.
> > what probably happened to John is, that his PV was killed by
> > this routine (they were duplicate and not md devices)
> 
> I would only think this is a problem when md isn't being used.  In the
> above described situation, vgscan would see 2 devices which have md
> headers (and ignore them), and one LVM signature (and use it)?

Correct!

> If the code does what you say, and LVM was using the dual-path SCSI
> device directly, then it would detect one and ignore the other, and it
> would still work as if there was only one route to the drive.

this is also correct, i was just guessing there might be another dragon
in this code, but we would need an output of vgscan -d from John to check.

> However, in this case, md is in the middle, and its md's job to handle
> multi-path.  LVM should be ignoring md's lowlevel volumes anyway, and
> act solely on the virtual device md exports.  Am I missing something?
John is not using md yet, you are correct in all you say.

Regards,
L.
-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
 / \

Re: [linux-lvm] LVM with multi-path disks?

[John DeFranco]

Hi,

So thanks for the replys so far. From some of the
replys I was not completely clear on what my issue.
I'll just cover everything in detail so avoid any
misunderstanding.

I have a fc connected hw raid box. I have three luns
defined in the raid box. It is connected to the host
by an Emulex controller and is using the emulex
lpfcdd light pulse driver. The raid box has two connections
to the host. So I see three luns on scsi2 and three on
scsi3 (as I would expect):

Host: scsi2 Channel: 00 Id: 111 Lun: 00
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
Host: scsi2 Channel: 00 Id: 111 Lun: 01
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
Host: scsi2 Channel: 00 Id: 111 Lun: 02
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
Host: scsi3 Channel: 00 Id: 109 Lun: 00
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
Host: scsi3 Channel: 00 Id: 109 Lun: 01
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
Host: scsi3 Channel: 00 Id: 109 Lun: 02
  Vendor: HP       Model: A6188A           Rev: HP01
  Type:   Direct-Access                    ANSI SCSI
revision: 03
[root@jack scsi]# 

This is a list of the device mapping:

bus       2         lpfc      CLAIMED
channel   2.0                 CLAIMED Id=?
target    2.0.111   tgt       CLAIMED
disk      2.0.111.0 sd        CLAIMED HP A6188A 
/dev/sdc /dev/sg3
disk      2.0.111.1 sd        CLAIMED HP A6188A 
/dev/sdd /dev/sg4
disk      2.0.111.2 sd        CLAIMED HP A6188A 
/dev/sde /dev/sg5
bus       3         lpfc      CLAIMED
channel   3.0                 CLAIMED Id=?
target    3.0.109   tgt       CLAIMED
disk      3.0.109.0 sd        CLAIMED HP A6188A 
/dev/sdf /dev/sg6
disk      3.0.109.1 sd        CLAIMED HP A6188A 
/dev/sdg /dev/sg7
disk      3.0.109.2 sd        CLAIMED HP A6188A 
/dev/sdh /dev/sg8
bus       1         sym53c8xx CLAIMED
[root@jack /root]# 

Disk /dev/sdc (/dev/sdf) is partitioned and part of a
vg. As things are now vgscan will not find the vg. I can
create one and it ok while the system is booted, but as
soon as I reboot I cannot see the vg anymore. I have
attached a vgscan -d output.

I'm not certain exactly how I would use md in this
context, and I'm not sure that I really want to since
I'm using hw raid.

Thanks!

Luca Berra wrote:
> 
> On Sun, Aug 05, 2001 at 12:32:57AM -0700, Mark Glines wrote:
> > On Sun, Aug 05, 2001 at 09:12:01AM +0200, Luca Berra wrote:
> > > there is an (*horrible*) piece of code in pv_read_all_pv.c
> > > that deals with multiple entries for the same PV, so all duplicate
> > > PV are skipped, so the md will be the obly one detected.
> > > what probably happened to John is, that his PV was killed by
> > > this routine (they were duplicate and not md devices)
> >
> > I would only think this is a problem when md isn't being used.  In the
> > above described situation, vgscan would see 2 devices which have md
> > headers (and ignore them), and one LVM signature (and use it)?
> 
> Correct!
> 
> > If the code does what you say, and LVM was using the dual-path SCSI
> > device directly, then it would detect one and ignore the other, and it
> > would still work as if there was only one route to the drive.
> 
> this is also correct, i was just guessing there might be another dragon
> in this code, but we would need an output of vgscan -d from John to check.
> 
> > However, in this case, md is in the middle, and its md's job to handle
> > multi-path.  LVM should be ignoring md's lowlevel volumes anyway, and
> > act solely on the virtual device md exports.  Am I missing something?
> John is not using md yet, you are correct in all you say.
> 
> Regards,
> L.
> --
> Luca Berra -- bluca@comedia.it
>         Communication Media & Services S.r.l.
>  /"\
>  \ /     ASCII RIBBON CAMPAIGN
>   X        AGAINST HTML MAIL
>  / \
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

-- 
==========
Cheers
   -jdf

Re: [linux-lvm] LVM with multi-path disks?

[Luca Berra]

On Sun, Aug 05, 2001 at 10:44:11AM -0700, John DeFranco wrote:
> I'm not certain exactly how I would use md in this
> context, and I'm not sure that I really want to since
> I'm using hw raid.
LVM does NOT have support for multipath.
in *redhat* kernels there is a patch that adds multipath support
to the md driver, you configure it as a raid-1 array, but it is
actually a multipath configuration.
it is the only way i know of doing what you want.

btw. i never tried this, i have an XP512 but i don't have a fc
card supported by linux on intel (should i tri with pa-linux?)

L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
 / \

Re: [linux-lvm] LVM with multi-path disks?

[Michael Lausch]

On 05 Aug 2001 20:25:58 +0200, Luca Berra wrote:
> On Sun, Aug 05, 2001 at 10:44:11AM -0700, John DeFranco wrote:
> > I'm not certain exactly how I would use md in this
> > context, and I'm not sure that I really want to since
> > I'm using hw raid.
> LVM does NOT have support for multipath.
> in *redhat* kernels there is a patch that adds multipath support
> to the md driver, you configure it as a raid-1 array, but it is
> actually a multipath configuration.
> it is the only way i know of doing what you want.
> 
> btw. i never tried this, i have an XP512 but i don't have a fc
> card supported by linux on intel (should i tri with pa-linux?)

The qlogic fibrechannel cards worke fine with an XP256 on HP lpr1000
servers (just for testing). There even exists a utility to show the
CDEV,LDEV of the LUN disks, so that it's not so easy to steal another
server's disk. 

> 
> L.
> 
> -- 
> Luca Berra -- bluca@comedia.it
>         Communication Media & Services S.r.l.
>  /"\
>  \ /     ASCII RIBBON CAMPAIGN
>   X        AGAINST HTML MAIL
>  / \
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

Re: [linux-lvm] LVM with multi-path disks?

[Ragnar Kjørstad]

On Sun, Aug 05, 2001 at 08:25:58PM +0200, Luca Berra wrote:
> in *redhat* kernels there is a patch that adds multipath support
> to the md driver, you configure it as a raid-1 array, but it is
> actually a multipath configuration.

If I remember correctly, you configure as "multipath" not "raid1". 

> it is the only way i know of doing what you want.
Another alternative is the linux-driver for the SUN T3. I haven't tried
it myself, but supposedly one can use the same driver for other
dual-path RAIDs as well.



-- 
Ragnar Kjorstad
Big Storage

Re: [linux-lvm] LVM with multi-path disks?

[John DeFranco]

Ragnar Kj�rstad wrote:
> 
> On Sun, Aug 05, 2001 at 08:25:58PM +0200, Luca Berra wrote:
> > in *redhat* kernels there is a patch that adds multipath support
> > to the md driver, you configure it as a raid-1 array, but it is
> > actually a multipath configuration.
> 
> If I remember correctly, you configure as "multipath" not "raid1".
> 
Do you know where the above is defined? I cannot find
anything in the raid documentation that talks about 
multipath?

> > it is the only way i know of doing what you want.
> Another alternative is the linux-driver for the SUN T3. I haven't tried
> it myself, but supposedly one can use the same driver for other
> dual-path RAIDs as well.
And I'm using something similiar to this driver, which
is what is giving me problems.

-- 
==========
Cheers
   -jdf

Re: [linux-lvm] LVM with multi-path disks?

[Ragnar Kjørstad]

On Mon, Aug 06, 2001 at 10:01:36AM -0700, John DeFranco wrote:
> Ragnar Kj�rstad wrote:
> > On Sun, Aug 05, 2001 at 08:25:58PM +0200, Luca Berra wrote:
> > > in *redhat* kernels there is a patch that adds multipath support
> > > to the md driver, you configure it as a raid-1 array, but it is
> > > actually a multipath configuration.
> > 
> > If I remember correctly, you configure as "multipath" not "raid1".
> 
> Do you know where the above is defined? I cannot find
> anything in the raid documentation that talks about 
> multipath?

You need to use the RH kernel to get the "multipath" option.
Unfortenately the md patch (from their source RPM) does not apply
cleanly to a standard kernel, and it didn't look trivial to fix :(



-- 
Ragnar Kjorstad
Big Storage

Re: [linux-lvm] LVM with multi-path disks?

[Tracy R Reed]

[-- Attachment #1: Type: text/plain, Size: 1388 bytes --]

On Sun, Aug 05, 2001 at 11:47:16PM +0200, Ragnar Kjørstad wrote:
> If I remember correctly, you configure as "multipath" not "raid1". 

Cool! I think I've heard about this patch once before. I will have to give
it a try.  Dual-pathing is something we have been wanting for a long time.
Do you think this patch something that is likely to one day be merged with
the kernel such that we can count on it being with us for a while?

> Another alternative is the linux-driver for the SUN T3. I haven't tried
> it myself, but supposedly one can use the same driver for other
> dual-path RAIDs as well.

Does anyone know of any driver for Clariion based disk arrays? I don't
think the Sun T3 uses Clariion does it? We have a ton (many tons,
literally :) that we are currently using with Solaris that we would love
to be able to attach to Linux systems. These things are hardware RAID
arrays with dual RAID controllers in them. When one RAID controller fails
something special has to be done to transfer the LUNs from the dead
controller over to the live one. They call this "ATF" or "Automatic
Transparent Failover" and they don't seem to ship it for Linux. Only NT
and Solaris. I've tried talking them into considering it but not had any
success.

-- 
Tracy Reed      http://www.ultraviolet.org
This is Linux Country. On a quiet night, you can hear Windows NT reboot!

[-- Attachment #2: Type: application/pgp-signature, Size: 240 bytes --]

Re: [linux-lvm] LVM with multi-path disks?

[Ragnar Kjørstad]

On Mon, Aug 06, 2001 at 06:46:31PM -0700, Tracy R Reed wrote:
> On Sun, Aug 05, 2001 at 11:47:16PM +0200, Ragnar Kj�rstad wrote:
> > If I remember correctly, you configure as "multipath" not "raid1". 
> 
> Cool! I think I've heard about this patch once before. I will have to give
> it a try.  Dual-pathing is something we have been wanting for a long time.
> Do you think this patch something that is likely to one day be merged with
> the kernel such that we can count on it being with us for a while?

I'm just speculating but I can't see why not? Except for LVM
implementing mutlipath and making it obsolete, of course.

> Does anyone know of any driver for Clariion based disk arrays? I don't
> think the Sun T3 uses Clariion does it? We have a ton (many tons,
> literally :) that we are currently using with Solaris that we would love
> to be able to attach to Linux systems. These things are hardware RAID
> arrays with dual RAID controllers in them. When one RAID controller fails
> something special has to be done to transfer the LUNs from the dead
> controller over to the live one. They call this "ATF" or "Automatic
> Transparent Failover" and they don't seem to ship it for Linux. Only NT
> and Solaris. I've tried talking them into considering it but not had any
> success.

Pardon me for finding it amusing they call it Automatic Transparent
Failover when it apperently is neither automatic nor transparent :-)


-- 
Ragnar Kjorstad
Big Storage

Re: [linux-lvm] LVM with multi-path disks?

[Carlo Marcelo Arenas Belon]

<SNIP>
> > arrays with dual RAID controllers in them. When one RAID controller fails
> > something special has to be done to transfer the LUNs from the dead
> > controller over to the live one. They call this "ATF" or "Automatic
> > Transparent Failover" and they don't seem to ship it for Linux. Only NT
> > and Solaris. I've tried talking them into considering it but not had any
> > success.
>
> Pardon me for finding it amusing they call it Automatic Transparent
> Failover when it apperently is neither automatic nor transparent :-)

well that is actually donde trasnparently by the driver, and not only when
one controller fails, but when there is a signal that there could be a
problem with the SP (Store Processor that connects to the disks) or even
with the SPS (battery that feeds the SP)

ATF is a pretty interesting hack, where you can virtualize the path to the
LUNs on a failover configuration, but it is not as good as EMC's PowerPath
(bundled with Symmetrix drivers) where you actually can do the same thing
and also share bandwith using the different paths at the same time.

i am not sure tough that this would be the right way to go as it is pretty
hardware specific and IMHO too low level, the same could be done on
software just like the Verita's DMP and probably the actual RedHat's
multipath capabilities for md could be just a step on the right direction.

just my 2c

Carlo

Re: [linux-lvm] LVM with multi-path disks?

[Tracy R Reed]

[-- Attachment #1: Type: text/plain, Size: 1609 bytes --]

On Tue, Aug 07, 2001 at 12:38:26AM -0500, Carlo Marcelo Arenas Belon wrote:
> ATF is a pretty interesting hack, where you can virtualize the path to the
> LUNs on a failover configuration, but it is not as good as EMC's PowerPath
> (bundled with Symmetrix drivers) where you actually can do the same thing
> and also share bandwith using the different paths at the same time.

Yes, it is interesting. Although we avoid the Symmetrix line because it's
even more closed than the Clariion arrays. We are very independent and
slice and dice harware to our liking. I sometimes think EMC finds us
frustrating to deal with because we are so independent when they are used
to holding the customers hand and not letting them touch the box. :) We
share bandwidth using the different paths at the same time by distributing
the LUNs equally over the two SP's.

> i am not sure tough that this would be the right way to go as it is pretty
> hardware specific and IMHO too low level, the same could be done on
> software just like the Verita's DMP and probably the actual RedHat's
> multipath capabilities for md could be just a step on the right direction.

Yes, it is definitely hardware specific. I was just wondering if anyone
happened to know of drivers for Linux. We have a ton of money invested in
many of these arrays and md's multipath won't work for us...unless I can
somehow bind a LUN to both SP's at the same time but I'm pretty sure that
is not possible.

-- 
Tracy Reed      http://www.ultraviolet.org
Bill Gates to his broker: "You idiot, I said $150 million on
**SNAPPLE**!!!"

[-- Attachment #2: Type: application/pgp-signature, Size: 240 bytes --]

Re: [linux-lvm] LVM with multi-path disks?

[Tracy R Reed]

[-- Attachment #1: Type: text/plain, Size: 897 bytes --]

On Tue, Aug 07, 2001 at 07:23:27AM +0200, Ragnar Kjørstad wrote:
> Pardon me for finding it amusing they call it Automatic Transparent
> Failover when it apperently is neither automatic nor transparent :-)

Actually, when installed properly on Solaris (easy to do) it actually is
automatic and transparent. I can shut down a RAID controller or yank the
fibre and it fails over to the other path and none of the applications
know it happened and the system keeps working as it should. We have it
installed on all of our Solaris systems with Clariion disk arrays. We have
never actually had a failover in production though. Overall it is very
nice but it is proprietary and expensive and requires a proprietary and
expensive Solaris or NT box to run it on.

-- 
Tracy Reed      http://www.ultraviolet.org
Bill Gates to his broker: "You idiot, I said $150 million on
**SNAPPLE**!!!"

[-- Attachment #2: Type: application/pgp-signature, Size: 240 bytes --]

Re: [linux-lvm] LVM with multi-path disks?

[Joe Thornber]

On Tue, Aug 07, 2001 at 07:23:27AM +0200, Ragnar Kjxrstad wrote:
> On Mon, Aug 06, 2001 at 06:46:31PM -0700, Tracy R Reed wrote:
> > On Sun, Aug 05, 2001 at 11:47:16PM +0200, Ragnar Kjxrstad wrote:
> > > If I remember correctly, you configure as "multipath" not "raid1". 
> > 
> > Cool! I think I've heard about this patch once before. I will have to give
> > it a try.  Dual-pathing is something we have been wanting for a long time.
> > Do you think this patch something that is likely to one day be merged with
> > the kernel such that we can count on it being with us for a while?
> 
> I'm just speculating but I can't see why not? Except for LVM
> implementing mutlipath and making it obsolete, of course.

In my opinion multipathing should be implemented outside LVM.

- Joe

Re: [linux-lvm] LVM with multi-path disks?

[Christoph Hellwig]

On Sun, Aug 05, 2001 at 02:28:01AM +0200, Ragnar Kj�rstad wrote:
> E.g. you have a md0 device consisting of sda and sdb - would not lvm
> find three different paths to the same data (sda, sdb, md0) when
> scanning for physical volumes? Will that not cause problems?

vgscan skips devices that are identified as md devices, so you will
not see sda and sdb but just md0.  Multipath is not different from
'normal' RAID in this respect.

	Christoph

-- 
Of course it doesn't work. We've performed a software upgrade.

Re: [linux-lvm] LVM with multi-path disks?

[Ragnar Kjørstad]

On Sun, Aug 05, 2001 at 11:06:07AM +0200, Christoph Hellwig wrote:
> On Sun, Aug 05, 2001 at 02:28:01AM +0200, Ragnar Kj�rstad wrote:
> > E.g. you have a md0 device consisting of sda and sdb - would not lvm
> > find three different paths to the same data (sda, sdb, md0) when
> > scanning for physical volumes? Will that not cause problems?
> 
> vgscan skips devices that are identified as md devices, so you will
> not see sda and sdb but just md0.  Multipath is not different from
> 'normal' RAID in this respect.

Hmm, I didn't think md devices needed superblocks thus could not be
identified?


-- 
Ragnar Kjorstad
Big Storage

Re: [linux-lvm] LVM with multi-path disks?

[Christoph Hellwig]

On Sun, Aug 05, 2001 at 11:47:39PM +0200, Ragnar Kj�rstad wrote:
> On Sun, Aug 05, 2001 at 11:06:07AM +0200, Christoph Hellwig wrote:
> > On Sun, Aug 05, 2001 at 02:28:01AM +0200, Ragnar Kj�rstad wrote:
> > > E.g. you have a md0 device consisting of sda and sdb - would not lvm
> > > find three different paths to the same data (sda, sdb, md0) when
> > > scanning for physical volumes? Will that not cause problems?
> > 
> > vgscan skips devices that are identified as md devices, so you will
> > not see sda and sdb but just md0.  Multipath is not different from
> > 'normal' RAID in this respect.
> 
> Hmm, I didn't think md devices needed superblocks thus could not be
> identified?

Humm, yeah you got me there ;)

For partitioned devices LVM will detect them because of the partition
id, but it will not detect unpartitioned devices.  So put one huge
partition on multipath disks for LVM to work.

On the other hand MD autodetect needs the partition table anyway..

	Christoph

-- 
Whip me.  Beat me.  Make me maintain AIX.

Re: [linux-lvm] LVM with multi-path disks?

[AJ Lewis]

[-- Attachment #1: Type: text/plain, Size: 1644 bytes --]

On Fri, Aug 03, 2001 at 04:16:20PM -0700, John DeFranco wrote:
> Does LVM work with multi-path disks? For example I have
> a fibre channel configuration in which I have two paths
> to each disk. I pvcreate a disk and am able to use it
> within a vg but when I reboot and do a vgscan, lvm cannot
> find any vg's. If I remove the second path lvm can see
> the vg fine.
> 
> Are there some configuration settings or such that need
> to be enabled?

Just to make it clear.  LVM does not currently have multipath support.  It
is planned for inclusion into LVM or possibly a separate driver to stack
with LVM after LVM 1.0 is released.

We are currently too busy dealing with trying to get a stable LVM release
out to start adding new features now, but hopefully multipathing and other
highly requested features will be supported soon.

For now it sounds like the best option is to patch MD to support
multipathing and stack LVM on top of that.

Regards,
-- 
AJ Lewis
Sistina Software Inc.                  Voice:  612-638-0500
1313 5th St SE, Suite 111              Fax:    612-638-0500
Minneapolis, MN 55414                  E-Mail: lewis@sistina.com
http://www.sistina.com

Current GPG fingerprint = 3B5F 6011 5216 76A5 2F6B  52A0 941E 1261 0029 2648
Get my key at: http://www.sistina.com/~lewis/gpgkey
 (Unfortunately, the PKS-type keyservers do not work with multiple sub-keys)

-----Begin Obligatory Humorous Quote----------------------------------------
Choose a job you love, and you will never have to work a day in your life.
-----End Obligatory Humorous Quote------------------------------------------

[-- Attachment #2: Type: application/pgp-signature, Size: 232 bytes --]

RE: [linux-lvm] LVM with multi-path disks?

[Gonyou, Austin]

Perhaps, if I can say, use the RH 7.2 kernel? It is 2.4.6 I believe. 

-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-796-9023
email: austin@coremetrics.com 

> -----Original Message-----
> From: Ragnar Kjørstad [mailto:lvm@ragnark.vestdata.no]
> Sent: Monday, August 06, 2001 12:26 PM
> To: linux-lvm@sistina.com
> Subject: Re: [linux-lvm] LVM with multi-path disks?
> 
> 
> On Mon, Aug 06, 2001 at 10:01:36AM -0700, John DeFranco wrote:
> > Ragnar Kjørstad wrote:
> > > On Sun, Aug 05, 2001 at 08:25:58PM +0200, Luca Berra wrote:
> > > > in *redhat* kernels there is a patch that adds multipath support
> > > > to the md driver, you configure it as a raid-1 array, but it is
> > > > actually a multipath configuration.
> > > 
> > > If I remember correctly, you configure as "multipath" not "raid1".
> > 
> > Do you know where the above is defined? I cannot find
> > anything in the raid documentation that talks about 
> > multipath?
> 
> You need to use the RH kernel to get the "multipath" option.
> Unfortenately the md patch (from their source RPM) does not apply
> cleanly to a standard kernel, and it didn't look trivial to fix :(
> 
> 
> 
> -- 
> Ragnar Kjorstad
> Big Storage
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> 

RE: [linux-lvm] LVM with multi-path disks?

[Gonyou, Austin]

Tracy,
  Possibly try GFS mounting..and then hosting GFS clienst?

-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-796-9023
email: austin@coremetrics.com 

> -----Original Message-----
> From: Tracy R Reed [mailto:treed@ultraviolet.org]
> Sent: Tuesday, August 07, 2001 2:41 AM
> To: linux-lvm@sistina.com
> Subject: Re: [linux-lvm] LVM with multi-path disks?
> 
> 
> On Tue, Aug 07, 2001 at 12:38:26AM -0500, Carlo Marcelo 
> Arenas Belon wrote:
> > ATF is a pretty interesting hack, where you can virtualize 
> the path to the
> > LUNs on a failover configuration, but it is not as good as 
> EMC's PowerPath
> > (bundled with Symmetrix drivers) where you actually can do 
> the same thing
> > and also share bandwith using the different paths at the same time.
> 
> Yes, it is interesting. Although we avoid the Symmetrix line 
> because it's
> even more closed than the Clariion arrays. We are very independent and
> slice and dice harware to our liking. I sometimes think EMC finds us
> frustrating to deal with because we are so independent when 
> they are used
> to holding the customers hand and not letting them touch the 
> box. :) We
> share bandwidth using the different paths at the same time by 
> distributing
> the LUNs equally over the two SP's.
> 
> > i am not sure tough that this would be the right way to go 
> as it is pretty
> > hardware specific and IMHO too low level, the same could be done on
> > software just like the Verita's DMP and probably the actual RedHat's
> > multipath capabilities for md could be just a step on the 
> right direction.
> 
> Yes, it is definitely hardware specific. I was just wondering 
> if anyone
> happened to know of drivers for Linux. We have a ton of money 
> invested in
> many of these arrays and md's multipath won't work for 
> us...unless I can
> somehow bind a LUN to both SP's at the same time but I'm 
> pretty sure that
> is not possible.
> 
> -- 
> Tracy Reed      http://www.ultraviolet.org
> Bill Gates to his broker: "You idiot, I said $150 million on
> **SNAPPLE**!!!"
>