I've set up a Raid 5 system at home for the first time. I've added 3 disks into the pc, and parted them all in 1 partition of 8G, and 1 partition of the remaining 492G then I made 2 raid volumes with each partition

Mounted the 16G as swap, and the other one as the system disk.

This worked like a charm, then I added a 4rd disk to the array did the same thing (parting in 2 partitions, and added both to the previously defined raid5 arrays) (mdadm --add /dev/sdd1 etc...)

Then I did the mdadm --grow /dev/md0 --raid-devices=4 command (ref: http://zackreed.me/articles/48-adding-an-extra-disk-to-an-mdadm-array)

Both arrays got rebuild, but they're not using the new size. and the performance of my system dropped terribly.

I've tried booting in recovery mode, and doing the resize2fs /dev/md1 command, but I keep getting "read only disk" stuff as issue.

How can I fix this? because normal boot will keep my main disk in "busy" status, and I've not dared doing a forced unmount

What can I do to get my performance back up?

If any more information is needed, do tell, and I'll supply what I can. Thx in advance.


Make sure you (1) unmount the file system for each array, and then (2) run:

e2fsck -f -v /dev/mdx

Where x is the array in question. Then run resize2fs. You should then be able to resize the file system.

In my experience, however, growing arrays (I grew one stepwise from 3+1 to ultimately 8+2 with 1TB disks over 2+ years) does seem to impact performance. This is possibly because things like strip size are dependent on the number of data disks (i.e., n-1 for RAID5, n-2 for RAID6) and thus will no longer be optimized for the new array.

Strip width = [Stride size] × [# Data Disks]

You'll want to address this with tune2fs afterwards, with something like:

tune2fs -E stride=n,stripe-width=m /dev/mdx

See this for more detail: https://raid.wiki.kernel.org/index.php/RAID_setup

  • Welcome to Ask Ubuntu! I've noticed you're using two separate unregistered accounts (which can happen if you're using the site without registering and the cookies that identify you are cleared). If you register an account, you can then use the contact form to request that all your accounts be merged. – Eliah Kagan Sep 7 '14 at 4:43

Your Answer

By clicking "Post Your Answer", you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.