On Tue, 23 Aug 2011 22:18:12 -0400 Mike Viau <viaum@xxxxxxxxxxxxxxx> wrote:
>
> > On Wed, 24 Aug 2011 <neilb@xxxxxxx> wrote:
> > > On Tue, 23 Aug 2011 19:41:11 -0400 Mike Viau <viaum@xxxxxxxxxxxxxxx> wrote:
> >
> > >
> > > Hello,
> > >
> > > I am trying to convert my currently running raid 5 array into a raid 1. All the guides I can see online are for the reverse direction in which one is converting/migrating a raid 1 to raid 5. I have intentionally only allocated exactly half of the total raid 5 size is. I would like to create the raid 1 over /dev/sdb1 and /dev/sdc1 with the data on the raid 5 running with the same drives plus /dev/sde1. Is this possible, I wish to have the data redundantly over two hard drive without the parity which is present in raid 5?
> >
> > Yes this is possible, though you will need a fairly new kernel (late 30's at
> > least) and mdadm.
> >
>
> In your opinion is Debian 2.6.32-35 going to cut it? Not very late 30's, with mdadm - v3.1.4 - 31st August 2010
Should be OK. The core functionality with in in 2.6.29. There have been a
few bug fixes since then but they are for corner cases that you probably
won't hit.
>
> > And you need to be running ext3 because I think it is the only one you can
> > shrink.
> >
> > 1/ umount filesystem
> > 2/ resize2fs /dev/md0 490G
> > This makes the array use definitely less than half the space. It is
> > safest to leave a bit of slack for relocated metadata or something.
> > If you don't make this small enough some later step will fail, and
> > you can then revert back to here and try again.
> >
>
>
> The file system used was ext4 which is mounted off of a LVM logical volume inside of a virtual machine :P
Nice of you to keep it simple...
ext4 isn't a problem. LVM shouldn't be, but it adds an extra step. You
first shrink the fs, then the lv, then the pv, then the RAID...
>
> I am still able to run the first two steps, but am considered about data loss on the underlying ext4 filesystem if I shrink the filesystem too much, 490G may not be possible. Other than that the following steps sound 'do-able' if the re-size works.
>
> > 3/ mdadm --grow --array-size=490G /dev/md0
> > This makes the array appear smaller without actually destroying any data.
> > 4/ fsck -f /dev/md0
> > This makes sure the filesystem inside the shrunk array is still OK.
> > If there is a problem you can "mdadm --grow" to a bigger size and check
> > again.
> >
> > Only if the above all looks ok, continue. You can remount the filesystem at
> > this stage if you want to.
> >
> > 5/ mdadm --grow /dev/md0 --raid-disks=2
> >
> > If you didn't make the array-size small enough, this will fail.
> > If you did it will start a 'reshape' which shuffles all the data around
> > so it fits (With parity) on just two devices.
> >
> > 6/ mdadm --wait /dev/md0
> > 7/ mdadm --grow /dev/md0 --level=1
> > This instantly converts a 2-device RAID5 to a 2-device RAID1.
> > 8/ mdadm --grow /dev/md0 --array-size=max
> > 9/ resize2fs /dev/md0
> > This will grow the filesystem up to fill the available space.
> >
> > All done.
> >
> > Please report success or failure or any interesting observations.
> >
>
> I am not sure how crack-pot of a solution this would be, but could I:
>
> 1/ mdadm -r /dev/md0 /dev/sde1
> Remove /dev/sde1 from the raid 5 array
Here you have lost your redundancy .... your choice I guess.
>
> 2/ dd if=/dev/zero of=/dev/sde1 bs=512 count=1
> This clears the msdos mbr and clears the partitions
>
> 3/ parted, fdisk or cfdisk to create a new 1TB (or less is possible as well) ext4 partition on /dev/sde
>
> 4/ mkfs.ext4 /dev/sde1
>
> 5/ cp -R {mounted location of degraded /dev/md0 partition} {mounted location of /dev/sde1 partition}
> Aka backup
>
> 6/ mdadm --zero-superblock on /dev/sdb1 and /dev/sdc1
> Prep the two drive for new raid array
Probably want to stop the array (mdadm -S /dev/md0) before you do that.
>
> 7/ mdadm create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
> Create new raid 1 array on drives
>
> 8/ create LVM (pv,vg, and lv)
>
> 9/ parted, fdisk or cfdisk to create a new 1TB ext4 partition on LVM
>
> 10/ mkfs.ext4 on LV on /dev/md0
>
> 11/ cp -R {mounted location of /dev/sde1 partition} {mounted location of new /dev/md0 partition}
>
> Any thought/suggestion/correction to this proposed idea?
Doing two copies seems a bit wasteful.
- fail/remove sdb1
- create a 1-device RAID1 on sdb1 (or a 2 device RAID1 with a missing device).
- do the lvm, mkfs
- copy from old filesystem to the new filesystem
- stop the old array.
- add sdc1 to the new RAID1.
- If you made it a 1-device RAID1, --grow it to 2 devices.
Only one copy operation needed.
NeilBrown
>
>
> Thanks again :)
>
> > >
> > >
> > > # mdadm -D /dev/md0
> > > /dev/md0:
> > > Version : 1.2
> > > Creation Time : Mon Dec 20 09:48:07 2010
> > > Raid Level : raid5
> > > Array Size : 1953517568 (1863.02 GiB 2000.40 GB)
> > > Used Dev Size : 976758784 (931.51 GiB 1000.20 GB)
> > > Raid Devices : 3
> > > Total Devices : 3
> > > Persistence : Superblock is persistent
> > >
> > > Update Time : Tue Aug 23 11:34:00 2011
> > > State : clean
> > > Active Devices : 3
> > > Working Devices : 3
> > > Failed Devices : 0
> > > Spare Devices : 0
> > >
> > > Layout : left-symmetric
> > > Chunk Size : 512K
> > >
> > > Name : HOST:0 (local to host HOST)
> > > UUID : 7d8a7c68:95a230d0:0a8f6e74:4c8f81e9
> > > Events : 55750
> > >
> > > Number Major Minor RaidDevice State
> > > 0 8 17 0 active sync /dev/sdb1
> > > 1 8 33 1 active sync /dev/sdc1
> > > 3 8 65 2 active sync /dev/sde1
> > >
> > >
> > > -M
>
>
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