Ubuntu – mdadm raid5 too slow when writing

mdadmraid5Ubuntu

I have set up a RAID5 array using 4 disk partition. All disks are 2TB. When the RAID5 array was initially syncing it was too slow. So I did a

echo 32768 > /sys/block/md2/md/stripe_cache_size

and then it was quiet fast. But still it took a days time to finish syncing. Now I want am doing a

dd if=/dev/zero of=/dev/md2 bs=1024k

onto the RAID5 array and it is like a day over and yet it has not finished. Will this take too much time am I doing some thing wrong.

My raid details are here http://dpaste.com/749742/
Iostat details here http://dpaste.com/749761/
hdd partitioning details here http://dpaste.com/749765/

I have an identical machine with the similar details. But that's quiet faster.

UPDATE: I have added my hdd partitioning details.

Best Answer

Normal time to build such array is 5.5-6 hours. There are a few things that can slow down array rebuild process - concurrent IO on the same disk, high cpu usage on the system, faulty HDD or cables.

dd if=/dev/zero of=/dev/md2 bs=1024k - will slow down rebuild. If you really need to rewrite your array with zeroes - do it after array has built.

Check if you have load on other partitions - using atop or iostat -nx 1

Check your load average in atop or top

Check for HDD errors in system logs and with smartctl.

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