Converting RAID5 to RAID0

Converting RAID5 to RAID0

[Mike Muratet]

I am doing some experiments with mdadm to combine two 1TB disks into a RAID
array. I used fdisk to create the partitions and mdadm to create a two disk
RAID5 array. I would like to have more space and I can live without
redundancy. I searched the man pages and boards for a way to do that and found:

$ sudo mdadm /dev/md0 -f /dev/sdd
mdadm: set /dev/sdd faulty in /dev/md0
$ sudo mdadm /dev/md0 -r /dev/sdd
mdadm: hot removed /dev/sdd from /dev/md0
$ sudo echo raid0 > /sys/block/md0/md/level

-bash: /sys/block/md0/md/level: Permission denied

which was not the result I expected.

Is it possible to convert RAID5 to RAID0?

There are no data on the disk. Is there a way to start over?

Cheers

Mike

Re: Converting RAID5 to RAID0

[Robin Hill]

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On Sun Aug 31, 2014 at 12:43:26PM +0000, Mike Muratet wrote:

> I am doing some experiments with mdadm to combine two 1TB disks into a RAID
> array. I used fdisk to create the partitions and mdadm to create a two disk
> RAID5 array. I would like to have more space and I can live without
> redundancy. I searched the man pages and boards for a way to do that and found:
> 
> $ sudo mdadm /dev/md0 -f /dev/sdd
> mdadm: set /dev/sdd faulty in /dev/md0
> $ sudo mdadm /dev/md0 -r /dev/sdd
> mdadm: hot removed /dev/sdd from /dev/md0
> $ sudo echo raid0 > /sys/block/md0/md/level
> 
> -bash: /sys/block/md0/md/level: Permission denied
> 
> which was not the result I expected.
> 
> Is it possible to convert RAID5 to RAID0?
> 
It should be, yes. I'd use "mdadm --grow --level=0" rather than direct
interaction with sysfs though. You may need to add "--force" in order to
get a 1-disk RAID0 array though (it's mentioned as being required for
create anyway).

> There are no data on the disk. Is there a way to start over?
> 
Sure. Just stop the arrays (mdadm -S /dev/md0) and then run a new create
command. You'll be prompted about an existing array (and filesystem, if
you'd created that) but can continue to overwrite with the new settings.

Cheers,
    Robin

-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: Converting RAID5 to RAID0

[NeilBrown]

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On Sun, 31 Aug 2014 12:43:26 +0000 (UTC) Mike Muratet <muratetm@gmail.com>
wrote:

> I am doing some experiments with mdadm to combine two 1TB disks into a RAID
> array. I used fdisk to create the partitions and mdadm to create a two disk
> RAID5 array. I would like to have more space and I can live without
> redundancy. I searched the man pages and boards for a way to do that and found:
> 
> $ sudo mdadm /dev/md0 -f /dev/sdd
> mdadm: set /dev/sdd faulty in /dev/md0
> $ sudo mdadm /dev/md0 -r /dev/sdd
> mdadm: hot removed /dev/sdd from /dev/md0
> $ sudo echo raid0 > /sys/block/md0/md/level
> 
> -bash: /sys/block/md0/md/level: Permission denied
> 
> which was not the result I expected.
> 
> Is it possible to convert RAID5 to RAID0?

Presumably you mean to convert a 2-device RAID5 to q 2-device RAID0, thus
doubling the amount of space.
  mdadm /dev/md0 --grow --level=0 --raid-disks=2

will tell you that you need a backup file, so
  mdadm /dev/md0 --grow --level=0 --raid-disks=2 --backup-file=/root/backup

will work... but will leave you with a degraded RAID4.  So just run that same
command again to finish the job.

NeilBrown



> 
> There are no data on the disk. Is there a way to start over?
> 
> Cheers
> 
> Mike
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


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Add disks and convert level 0 to level 5

[Michael Muratet]

I have a two-disk RAID0 system that is working splendidly, thanks to the list for the help.

I managed to get my hands on more identical disks and since I have the disks and because I'm adding precious data, I'd like to add two more disks and grow to RAID5.

I have partitioned the two new drives to type 'fd', /dev/sde and /dev/sdf

I believe the command to accomplish the change is this:

mdadm /dev/md0 --grow --level=5 --add /dev/sde /dev/sdf

Following the old adage "measure twice, cut once", is this syntax correct? Is there any danger of data loss in such a conversion?

Thanks

Mike

Re: Add disks and convert level 0 to level 5

[NeilBrown]

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On Wed, 10 Sep 2014 11:15:24 -0500 Michael Muratet <muratetm@gmail.com> wrote:

> I have a two-disk RAID0 system that is working splendidly, thanks to the list for the help.
> 
> I managed to get my hands on more identical disks and since I have the disks and because I'm adding precious data, I'd like to add two more disks and grow to RAID5.
> 
> I have partitioned the two new drives to type 'fd', /dev/sde and /dev/sdf
> 
> I believe the command to accomplish the change is this:
> 
> mdadm /dev/md0 --grow --level=5 --add /dev/sde /dev/sdf
> 
> Following the old adage "measure twice, cut once", is this syntax correct? Is there any danger of data loss in such a conversion?

I recommend creating a few loop-back devices and experimenting.
i.e.:
  create some 100M files.
  use "losetup" to turn them into block devices.
  create an 2-device raid0
  try converting it as you suggest.

You find it doesn't do quite what you expected, but should be easy to fix.

Providing your new devices are reliable (as least read/write the entire drive
once if you feel at all cautious) there is no particular danger of data loss.

NeilBrown


> 
> Thanks
> 
> Mike--
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


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Re: Add disks and convert level 0 to level 5

[Michael Muratet]

On Sep 10, 2014, at 7:27 PM, NeilBrown wrote:

> On Wed, 10 Sep 2014 11:15:24 -0500 Michael Muratet <muratetm@gmail.com> wrote:
> 
>> I have a two-disk RAID0 system that is working splendidly, thanks to the list for the help.
>> 
>> I managed to get my hands on more identical disks and since I have the disks and because I'm adding precious data, I'd like to add two more disks and grow to RAID5.
>> 
>> I have partitioned the two new drives to type 'fd', /dev/sde and /dev/sdf
>> 
>> I believe the command to accomplish the change is this:
>> 
>> mdadm /dev/md0 --grow --level=5 --add /dev/sde /dev/sdf
>> 
>> Following the old adage "measure twice, cut once", is this syntax correct? Is there any danger of data loss in such a conversion?
> 
> I recommend creating a few loop-back devices and experimenting.
> i.e.:
>  create some 100M files.
>  use "losetup" to turn them into block devices.
>  create an 2-device raid0
>  try converting it as you suggest.
> 
> You find it doesn't do quite what you expected, but should be easy to fix.

In case anyone wants to do a similar thing...

As predicted, it did not do as I expected. I have another identical server and disks and so I did the experiment there.

  980  sudo fdisk /dev/sdc
  981  sudo fdisk /dev/sdd
  982  sudo fdisk /dev/sde
  983  sudo fdisk /dev/sdf
  988  sudo partprobe /dev/sdc
  989  sudo partprobe /dev/sdd
  990  sudo partprobe /dev/sde
  991  sudo partprobe /dev/sdf
  995  sudo mdadm --create /dev/md0 --level=0 --raid-disk=2 /dev/sdc1 /dev/sdd1
  996  sudo mkfs -t ext3 /dev/md0
  997  sudo mount -t ext3 /dev/md0 /db

Same RAID0 system I created before. Now to grow

 1004  sudo mdadm /dev/md0 --grow --level=5 --add /dev/sde1 /dev/sdf1

Makes a RAID5 system, but sde1 was added as a spare

 1022  sudo mdadm --grow /dev/md0 --raid-devices=4

It's now a four disk RAID, but smaller than expected. It spread the original space over four drives, which I think is the documented behavior.

 1040  sudo umount /dev/md0
 1045  sudo e2fsck -f /dev/md0
 1046  sudo resize2fs -p /dev/md0
 1048  sudo mount -t ext3 /dev/md0 /db
 1049  df -h

/dev/md0                      2.7T  202M  2.6T   1% /db

which is what I wanted. I can't take my original system offline now, but when I can I will apply the same steps.

Thanks for the help

Cheers

Mike
> 
> Providing your new devices are reliable (as least read/write the entire drive
> once if you feel at all cautious) there is no particular danger of data loss.
> 
> NeilBrown
> 
> 
>> 
>> Thanks
>> 
>> Mike--
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: Add disks and convert level 0 to level 5

[Robin Hill]

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On Wed Sep 17, 2014 at 09:59:00am -0500, Michael Muratet wrote:

> 
> On Sep 10, 2014, at 7:27 PM, NeilBrown wrote:
> 
> > On Wed, 10 Sep 2014 11:15:24 -0500 Michael Muratet <muratetm@gmail.com> wrote:
> > 
> >> I have a two-disk RAID0 system that is working splendidly, thanks
> >> to the list for the help.
> >> 
> >> I managed to get my hands on more identical disks and since I have
> >> the disks and because I'm adding precious data, I'd like to add two
> >> more disks and grow to RAID5.
> >> 
> >> I have partitioned the two new drives to type 'fd', /dev/sde and /dev/sdf
> >> 
> >> I believe the command to accomplish the change is this:
> >> 
> >> mdadm /dev/md0 --grow --level=5 --add /dev/sde /dev/sdf
> >> 
> >> Following the old adage "measure twice, cut once", is this syntax
> >> correct? Is there any danger of data loss in such a conversion?
> > 
> > I recommend creating a few loop-back devices and experimenting.
> > i.e.:
> >  create some 100M files.
> >  use "losetup" to turn them into block devices.
> >  create an 2-device raid0
> >  try converting it as you suggest.
> > 
> > You find it doesn't do quite what you expected, but should be easy to fix.
> 
> In case anyone wants to do a similar thing...
> 
> As predicted, it did not do as I expected. I have another identical
> server and disks and so I did the experiment there.
> 
>   980  sudo fdisk /dev/sdc
>   981  sudo fdisk /dev/sdd
>   982  sudo fdisk /dev/sde
>   983  sudo fdisk /dev/sdf
>   988  sudo partprobe /dev/sdc
>   989  sudo partprobe /dev/sdd
>   990  sudo partprobe /dev/sde
>   991  sudo partprobe /dev/sdf
>   995  sudo mdadm --create /dev/md0 --level=0 --raid-disk=2 /dev/sdc1 /dev/sdd1
>   996  sudo mkfs -t ext3 /dev/md0
>   997  sudo mount -t ext3 /dev/md0 /db
> 
> Same RAID0 system I created before. Now to grow
> 
>  1004  sudo mdadm /dev/md0 --grow --level=5 --add /dev/sde1 /dev/sdf1
> 
> Makes a RAID5 system, but sde1 was added as a spare
> 
>  1022  sudo mdadm --grow /dev/md0 --raid-devices=4
> 
You should be able to combine the above into a single command (it worked
for me on loopback devices anyway):
    sudo mdadm --grow /dev/md0 --level=5 --raid-devices=4 \
               --add /dev/sde1 /dev/sdf1

> It's now a four disk RAID, but smaller than expected. It spread the
> original space over four drives, which I think is the documented
> behavior.
> 
As md has no knowledge of the filesystem or how to change the size of
it, then all it can do it redistribute the original data over the
additional disks. The md device size should have increased though, even
if the filesystem size hadn't.

>  1040  sudo umount /dev/md0
>  1045  sudo e2fsck -f /dev/md0
>  1046  sudo resize2fs -p /dev/md0
>  1048  sudo mount -t ext3 /dev/md0 /db
>  1049  df -h
> 
> /dev/md0                      2.7T  202M  2.6T   1% /db
> 
> which is what I wanted. I can't take my original system offline now,
> but when I can I will apply the same steps.
> 
You shouldn't need to take it offline - resize2fs works perfectly well
online.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: Add disks and convert level 0 to level 5

[Robin Hill]

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On Wed Sep 10, 2014 at 11:15:24AM -0500, Michael Muratet wrote:

> I have a two-disk RAID0 system that is working splendidly, thanks to
> the list for the help.
> 
> I managed to get my hands on more identical disks and since I have the
> disks and because I'm adding precious data, I'd like to add two more
> disks and grow to RAID5.
> 
> I have partitioned the two new drives to type 'fd', /dev/sde and /dev/sdf
> 
> I believe the command to accomplish the change is this:
> 
> mdadm /dev/md0 --grow --level=5 --add /dev/sde /dev/sdf
> 
If you've partitioned the drives then presumably you'd want to use the
partitions here (/dev/sde1 and /dev/sdf1?) rather than the full drives.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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