[linux-lvm] Problem with LVM over RAID-1

[linux-lvm] Problem with LVM over RAID-1

[Urs Thuermann]

This problem has occrued on this mailing list before by another user
but I haven't read a solution to it here.

We want to setup LVM over a RAID-1 array, i.e. LVM on /dev/md0.  But
the pvcreate on /dev/md0 fails:


    oker:~# uname -a
    Linux oker 2.4.7oker #1 SMP Sat Oct 13 18:31:47 CEST 2001 i586 unknown
    oker:~# dmesg|grep -i lvm
    LVM version 0.9.1_beta2  by Heinz Mauelshagen  (18/01/2001)
    lvm -- Driver successfully initialized
    oker:~# pvcreate --version
    pvcreate: Logical Volume Manager 1.0.1-rc3
    Heinz Mauelshagen, Sistina Software  01/10/2001 (IOP 10)
    oker:~# grep md/0 /proc/partitions 
       9     0   17775808 md/0
    oker:~# pvcreate -v /dev/md0
    pvcreate -- locking logical volume manager
    pvcreate -- checking physical volume name "/dev/md0"
    pvcreate -- getting physical volume size
    pvcreate -- device "/dev/md0" has a partition table
    
    
    pvcreate [-d|--debug] [-f[f]|--force [--force]] [-h|--help] [-y|--yes]
    	    [-v|--verbose] [--version] PhysicalVolume [PhysicalVolume...]
    
    oker:~# dd if=/dev/zero of=/dev/md0 count=256 bs=512
    256+0 records in
    256+0 records out
    oker:~# pvcreate -v /dev/md0
    pvcreate -- locking logical volume manager
    pvcreate -- checking physical volume name "/dev/md0"
    pvcreate -- getting physical volume size
    pvcreate -- device "/dev/md0" has a partition table
    
    
    pvcreate [-d|--debug] [-f[f]|--force [--force]] [-h|--help] [-y|--yes]
    	    [-v|--verbose] [--version] PhysicalVolume [PhysicalVolume...]
    

However, /dev/md0 seems to be ok.  I can dd to/from it, I can mkfs on
it.  The RAID-array is configured as

    oker:~# cat /etc/raidtab 
    raiddev /dev/md0
    	    raid-level              1
    	    nr-raid-disks           2
    	    nr-spare-disks          0
    	    chunk-size              4
    	    persistent-superblock   1
    	    device                  /dev/sdb3
    	    raid-disk               0
    	    device                  /dev/sda3
    	    failed-disk             1

/dev/sda3 is marked as "failed" currently, since there is now an ext2
FS on sda3 on which the system was installed and is currently running
(debain sid, BTW).  We plan to install LVM on /dev/md0, copy
everything over to it and then mirror sdb3 to sda3.

Can anyone help us with creating a PV on /dev/md0, please?
    

Another question on Linux-Software RAID-1:  We want to use it to get
more reliability by mirroring.  But I'd like to know if the Linux
kernel will also make use of both disks to increase the read
performance, i.e. when reading a large file, read some parts from one
disk, other parts from the other disk.  Or when accessing two files,
read one file from one disk and the other file from the second disk.
Will the Linux kernel do this?


urs

Re: [linux-lvm] Problem with LVM over RAID-1

[svetljo]

>
>
>LVM version 0.9.1_beta2  by Heinz Mauelshagen  (18/01/2001)
>    lvm -- Driver successfully initialized
>    oker:~# pvcreate --version
>    pvcreate: Logical Volume Manager 1.0.1-rc3
>    Heinz Mauelshagen, Sistina Software  01/10/2001 (IOP 10)
>
>    pvcreate -- device "/dev/md0" has a partition table
>
my guess is, try with lvm-1.0.1rc4 but patch the kernel too
i had the same problems and this solved them
if this doesn't help you can try instaling a Mandrake partitioning tool
diskdrake, with the older version you could change the partition id of 
md to 8e (lvm)
but sadly the current version doesn't support it

good luck

>    
>

Re: [linux-lvm] Problem with LVM over RAID-1

[José Luis Domingo López]

On Sunday, 14 October 2001, at 11:01:10 +0200,
Urs Thuermann wrote:

> This problem has occrued on this mailing list before by another user
> but I haven't read a solution to it here.
> [...]
> Another question on Linux-Software RAID-1:  We want to use it to get
> more reliability by mirroring.  But I'd like to know if the Linux
> kernel will also make use of both disks to increase the read
> performance, i.e. when reading a large file, read some parts from one
> disk, other parts from the other disk.  Or when accessing two files,
> read one file from one disk and the other file from the second disk.
> Will the Linux kernel do this?
> 
As far as I remember, Linux software RAID-1 implementation indeed uses all
of the drives in parallel to increase read performance (at least, on 2.2.x
an 2.4.x kernels). As read on Software-RAID-HOWTO (2.3. The RAID levels):

    * Write performance is the slightly worse than on a single device,
	* because identical copies of the data written must be sent to every
	* disk in the array. Read performance is usually pretty bad because of
	* an oversimplified read-balancing strategy in the RAID code. However,
	* there has been implemented a much improved read-balancing strategy,
	* which might be available for the Linux-2.2 RAID patches (ask on the
	* linux-kernel list), and which will most likely be in the standard
	* 2.4 kernel RAID support.

So, to be sure, you should build a RAID-1 array with your current kernel
and test read performance, and compare results with those for a single
drive (use bonnie, for example). Maybe in the linux-raid mailing list
archives is something interesting:
http://www.mail-archive.com/linux-raid%40vger.kernel.org

-- 
Jos� Luis Domingo L�pez
Linux Registered User #189436     Debian Linux Woody (P166 64 MB RAM)
 
jdomingo EN internautas PUNTO org  => � Spam ? Atente a las consecuencias
jdomingo AT internautas DOT   org  => Spam at your own risk

RE: [linux-lvm] Problem with LVM over RAID-1

[yves.alloyer]

You may want to look at the  "[linux-lvm] pvcreate fails on a software RAID
metadisk" thread.
There is something going wrong in lvm_check_partitioned_dev.
AFAIK the problem is being investigated. Since you probably don't want to
partition any of your MD devices, the following patch should do it. It just
tells LVM to use the whole device.
I've got that running... (2.4.10/1.0.1-rc4).
Hope it helps.
Yves
------------------------------------------------------------------------
--- tools/lib/lvm_check_partitioned_dev.c.bluca	Thu Aug 23 07:51:53 2001
+++ tools/lib/lvm_check_partitioned_dev.c	Fri Oct  5 21:18:51 2001
@@ -55,6 +55,8 @@
 	switch (lvm_get_device_type(st_rdev)) {
 	case LVM_DEVICE_TYPE_INVALID:
 	    break;
+	case LVM_DEVICE_TYPE_MD:
+	    break;
 	default:
 	    ret = TRUE;
 	}
------------------------------------------------------------------------

> -----Original Message-----
> From: linux-lvm-admin@sistina.com [mailto:linux-lvm-admin@sistina.com]On
> Behalf Of Urs Thuermann
> Sent: Sunday, October 14, 2001 11:01 AM
> To: linux-lvm@sistina.com
> Subject: [linux-lvm] Problem with LVM over RAID-1
>
>
> This problem has occrued on this mailing list before by another user
> but I haven't read a solution to it here.
>
> We want to setup LVM over a RAID-1 array, i.e. LVM on /dev/md0.  But
> the pvcreate on /dev/md0 fails:
>
>
>     oker:~# uname -a
>     Linux oker 2.4.7oker #1 SMP Sat Oct 13 18:31:47 CEST 2001 i586 unknown
>     oker:~# dmesg|grep -i lvm
>     LVM version 0.9.1_beta2  by Heinz Mauelshagen  (18/01/2001)
>     lvm -- Driver successfully initialized
>     oker:~# pvcreate --version
>     pvcreate: Logical Volume Manager 1.0.1-rc3
>     Heinz Mauelshagen, Sistina Software  01/10/2001 (IOP 10)
>     oker:~# grep md/0 /proc/partitions
>        9     0   17775808 md/0
>     oker:~# pvcreate -v /dev/md0
>     pvcreate -- locking logical volume manager
>     pvcreate -- checking physical volume name "/dev/md0"
>     pvcreate -- getting physical volume size
>     pvcreate -- device "/dev/md0" has a partition table
>
>
>     pvcreate [-d|--debug] [-f[f]|--force [--force]] [-h|--help] [-y|--yes]
>     	    [-v|--verbose] [--version] PhysicalVolume [PhysicalVolume...]
>
>     oker:~# dd if=/dev/zero of=/dev/md0 count=256 bs=512
>     256+0 records in
>     256+0 records out
>     oker:~# pvcreate -v /dev/md0
>     pvcreate -- locking logical volume manager
>     pvcreate -- checking physical volume name "/dev/md0"
>     pvcreate -- getting physical volume size
>     pvcreate -- device "/dev/md0" has a partition table
>
>
>     pvcreate [-d|--debug] [-f[f]|--force [--force]] [-h|--help] [-y|--yes]
>     	    [-v|--verbose] [--version] PhysicalVolume [PhysicalVolume...]
>
>
> However, /dev/md0 seems to be ok.  I can dd to/from it, I can mkfs on
> it.  The RAID-array is configured as
>
>     oker:~# cat /etc/raidtab
>     raiddev /dev/md0
>     	    raid-level              1
>     	    nr-raid-disks           2
>     	    nr-spare-disks          0
>     	    chunk-size              4
>     	    persistent-superblock   1
>     	    device                  /dev/sdb3
>     	    raid-disk               0
>     	    device                  /dev/sda3
>     	    failed-disk             1
>
> /dev/sda3 is marked as "failed" currently, since there is now an ext2
> FS on sda3 on which the system was installed and is currently running
> (debain sid, BTW).  We plan to install LVM on /dev/md0, copy
> everything over to it and then mirror sdb3 to sda3.
>
> Can anyone help us with creating a PV on /dev/md0, please?
>
>
> Another question on Linux-Software RAID-1:  We want to use it to get
> more reliability by mirroring.  But I'd like to know if the Linux
> kernel will also make use of both disks to increase the read
> performance, i.e. when reading a large file, read some parts from one
> disk, other parts from the other disk.  Or when accessing two files,
> read one file from one disk and the other file from the second disk.
> Will the Linux kernel do this?
>
>
> urs
>
> _______________________________________________
> 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] Problem with LVM over RAID-1

[Luca Berra]

On Mon, Oct 15, 2001 at 01:02:26PM +0200, yves.alloyer wrote:
> You may want to look at the  "[linux-lvm] pvcreate fails on a software RAID
> metadisk" thread.
the fix mentioned by Yves has been checked into CVS.
please check instructions at http://www.sistina.com/products_CVS.htm
to use current CVS version

L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
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RE: [linux-lvm] Problem with LVM over RAID-1

[yves.alloyer]

Sorry, didn't know that.
Yves

> -----Original Message-----
> From: linux-lvm-admin@sistina.com [mailto:linux-lvm-admin@sistina.com]On
> Behalf Of Luca Berra
> Sent: Monday, October 15, 2001 2:08 PM
> To: linux-lvm@sistina.com
> Subject: Re: [linux-lvm] Problem with LVM over RAID-1
> 
> 
> On Mon, Oct 15, 2001 at 01:02:26PM +0200, yves.alloyer wrote:
> > You may want to look at the  "[linux-lvm] pvcreate fails on a 
> software RAID
> > metadisk" thread.
> the fix mentioned by Yves has been checked into CVS.
> please check instructions at http://www.sistina.com/products_CVS.htm
> to use current CVS version
> 
> 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] Problem with LVM over RAID-1

[Urs Thuermann]

"yves.alloyer" <Yves.ALLOYER@slpinfoware.com> writes:

> There is something going wrong in lvm_check_partitioned_dev.
> AFAIK the problem is being investigated. Since you probably don't want to
> partition any of your MD devices, the following patch should do it. It just
> tells LVM to use the whole device.
> I've got that running... (2.4.10/1.0.1-rc4).
> Hope it helps.

Thank you (and all others you have replied to my question).  We have
looked into the source, too, and did a similar but very dirty patch,
just to get it to work.  We just inserted a return 0.  We'll consider
upgrading to the CVS version.

Thanks again
urs