Simple Raid-1 setup question

DISCUSSION Kurt Newman 3 participants 4 messages Nov 13, 2009 MD RAID

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Kurt Newman

author

2009-11-13 20:34 UTC #0 lore raw

My questions are as follows:

1) If you're creating a completely new array (e.g. raid-1) on new partitions that aren't formatted, do you still have to sync? I'm having difficulty finding information on why and when a sync is needed. I was under the impression a sync is only needed when there's existing information on one or more of the drives.

2) If there used to be information on each device, but has since been repartitioned, so that new partitions and a raid device can be created... is there any way to prevent mdadm from asking if you really want to create the array? Using `--force' doesn't seem to help.

mdadm: /dev/sda1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
mdadm: /dev/sdb1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
Continue creating array?

As a side note, there really isn't an existing ext3 fs on it, but there used to be. To re-use the device, I issued the following commands:

Quoted 2 lines

parted -s /dev/sda mklabel msdos
parted -s /dev/sda mkpart primary ext3 0 1500

Majed B.

2009-11-13 21:02 UTC #1 lore raw

1) No need to sync if both disks are new (or have no data). That can be accomplished using: --assume-clean

2) It shouldn't be a problem. If you still can't force mdadm, use dd (be very sure you're writing to the correct disks!!)
dd if=/dev/zero of=/dev/sdx bs=10M count=1

That will write 10MB of zeros to the disk. It should corrupt any filesystem laying there.

Remember to change the partition type to "FD" for RAID auto-detect.

Create your filesystem on the array after you create it & that's it.

Quoted 29 lines · Kurt Newman

My questions are as follows:
1) If you're creating a completely new array (e.g. raid-1) on new partitions that aren't formatted, do you still have to sync? I'm having difficulty finding information on why and when a sync is needed. I was under the impression a sync is only needed when there's existing information on one or more of the drives.
2) If there used to be information on each device, but has since been repartitioned, so that new partitions and a raid device can be created... is there any way to prevent mdadm from asking if you really want to create the array? Using `--force' doesn't seem to help.
mdadm: /dev/sda1 appears to contain an ext2fs file system size=1464840K mtime=Fri Nov 13:04:09 2009
mdadm: /dev/sdb1 appears to contain an ext2fs file system size=1464840K mtime=Fri Nov 13:04:09 2009 Continue creating array?
As a side note, there really isn't an existing ext3 fs on it, but there used to be. To re-use the device, I issued the following commands:
> parted -s /dev/sda mklabel msdos
> parted -s /dev/sda mkpart primary ext3 0 1500
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Signature · 5 lines

       Majed B.
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Kurt Newman

author

2009-11-13 23:26 UTC #2 lore raw

That clears up a lot of my questions. Although, --assume-clean isn't doing what I'd like, I did some searches using the keyword, '--assume-clean'. That lead me back to the linux raid wiki.

Apparently I lack the ability to read 'Initial Array Creation' the last time I was there.

Thank you for the help.

Quoted 47 lines · Majed B.

1) No need to sync if both disks are new (or have no data). That can be accomplished using: --assume-clean
2) It shouldn't be a problem. If you still can't force mdadm, use dd (be very sure you're writing to the correct disks!!)
dd if=/dev/zero of=/dev/sdx bs=10M count=1
That will write 10MB of zeros to the disk. It should corrupt any filesystem laying there.
Remember to change the partition type to "FD" for RAID auto-detect.
Create your filesystem on the array after you create it & that's it.
Quoted 29 lines · Kurt Newman
My questions are as follows:
1) If you're creating a completely new array (e.g. raid-1) on new partitions that aren't formatted, do you still have to sync? I'm having difficulty finding information on why and when a sync is needed. I was under the impression a sync is only needed when there's existing information on one or more of the drives.
2) If there used to be information on each device, but has since been repartitioned, so that new partitions and a raid device can be created... is there any way to prevent mdadm from asking if you really want to create the array? Using `--force' doesn't seem to help.
mdadm: /dev/sda1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
mdadm: /dev/sdb1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
Continue creating array?
As a side note, there really isn't an existing ext3 fs on it, but there used to be. To re-use the device, I issued the following commands:
Quoted 2 lines
parted -s /dev/sda mklabel msdos
parted -s /dev/sda mkpart primary ext3 0 1500
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Neil Brown

2009-11-13 22:24 UTC #3 lore raw

In reply to Kurt Newman

Quoted 7 lines · On Friday November 13, [email protected] wrote:

My questions are as follows:
1) If you're creating a completely new array (e.g. raid-1) on new partitions that aren't formatted, do you still have to sync? I'm having difficulty finding information on why and when a sync is needed. I was under the impression a sync is only needed when there's existing information on one or more of the drives.

You don't need to for RAID1 - you do for RAID5.
If you don't with RAID1, then the first time you run a 'check' to 'scrub' the array, it might report lots of differences in mismatch_cnt.

Quoted 5 lines

2) If there used to be information on each device, but has since been repartitioned, so that new partitions and a raid device can be created... is there any way to prevent mdadm from asking if you really want to create the array? Using `--force' doesn't seem to help.

use -R or --run if you are really sure.

NeilBrown

Quoted 16 lines

mdadm: /dev/sda1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
mdadm: /dev/sdb1 appears to contain an ext2fs file system
size=1464840K mtime=Fri Nov 13:04:09 2009
Continue creating array?
As a side note, there really isn't an existing ext3 fs on it, but there used to be. To re-use the device, I issued the following commands:
Quoted 2 lines
parted -s /dev/sda mklabel msdos
parted -s /dev/sda mkpart primary ext3 0 1500
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html