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I am building a home server with raid 5. I first set up the system to boot from compact flash. After i got that working I tried to create the raid 5 array. All disks are new and have no data on them. I used the following command to create the array:

mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sd[bcd]1

After this I ran 'watch cat /proc/mdstat'. The system is recovering - very very slowly (like 40 hours to recover).

How do I tell the system these are new disks with no user data on? I don't want to recover anything.

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Unfortunately that's just part of the joyous mdadm build process. At least that's been my experience of it... But I have only done it twice.

You can speed things up by increasing the stripe cache

sudo su
echo 8192 > /sys/block/md0/md/stripe_cache_size

You can run that now and it should have near-immediate effect.

That won't persist between restarts but if it does improve performance, you can make it.

  • Thanks! that has made a massive difference. I have favourited your question about making it persistant. I hope you get an answer. By the way - does this value effect the calculations used to optimse mkfs.xfs or mkfs.ext4? There you basically double the chunk size / stripe size for the sunit value. – Amir Feb 24 '12 at 2:20

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