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consider you are creating a raid5 device with three drives.

mdadm --create /dev/md0 --leve=5 --raid-disk=3 /dev/sda1 /dev/sdb1 /dev/sdc1

After issuing this command , I can see the progress of md device creating using cat /proc/mdstat.

During the progress ITSELF, can I create a file ssytem partition say ext2 on md0 device like: mkfs.ext2 /dev/md0.

Actually I am able to create this and want to confirm whether doing this before 100% completion of md device creation is CORRECT?

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Actually I am able to create this and want to confirm whether doing this before 100% completion of md device creation is CORRET?

It is fine to create the filesystem immediately after creating the volume.

Until the array is 100% synced up there will be performance degradation when you try to use the volume. So creating the filesystem will slow down the initial sync a bit. If you actually try to use the volume while the sync is happening, then I/O operations will be slow.

Until the array is 100% synced up, it will basically act like a RAID0, meaning that you will have stripping and no parity. Meaning that you if you create a filesystem, and put important data on it, and one of the drive fails during the initial sync, you will lose all your data.

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Thanks for your detailed answer –  kumar Jul 1 '11 at 6:09

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