I just upgraded and reinstalled my home server. One thing I did was going from software raid to a raid card.

After doing this and starting to copy back my backups, I've noticed that my first ~1TB backup takes up ~1.4TB of space on my new array. Since thats a whopping 400GB increase in space used, I'm guessing I've done something wrong.

My setup

I have my OS installed on a separate 32GB SSD. All drives used in the array are WD Red 2TB WD20EFRX.

My old setup was on Ubuntu 14.04 Desktop with a 3x2TB RAID-5 array (leaving 4TB available). I was using the software raid function in my motherboards BIOS. I had partitioned and formated the array using the Disk Utility in GNOME. I'm not sure what format I used. It was most likely what was presented as default for me.

My new setup is on Ubuntu 14.10 Server. The array is now a 6x2TB RAID-5 array (leaving 10TB available in theory). I'm now using the RocketRaid 2720SGL "fake hardware" raid card.

Setup process

I installed the driver and WebGUI and then initialised the drives and created the new RAID-5 array through the RocketRaid WebGUI (which I read in reviews was strongly recommended over the cards BIOS function). Being unsure on the more advanced settings, I picked the default sector size of 512B. The build process ran through the night successfully.

Using fdisk I then partitioned the array. Due to the size of the disk fdisk warned me that I needed to select the GUID partition table - which I did. I formated the array as ext4 (seemed the recommended choice from my research). For sector size, sector start and sector end I picked the default values presented to me.

Using fdisk -l it looks like this right now

Device    Start         End     Sectors Size Type
/dev/sdb1 2048  19534315486 19534313439 9.1T Linux filesystem

I initially looked at picking 4K instead of 512B when building the array. However when I researched the drives I use I found some debate concerning getting 4K sector size to work on them, so I decided against it.

I had my original array backed up on 3 different external 1TB drives. I had copied ~980GB chunk of directories from the original array to the first external drive (the external drive is formated as ext4). Restoring from this external drive I connected the drive via USB to the server and mounted it to /media/usb. I then used this command to copy the backup from the first external drive to my new array.

rsync -av /media/usb /media/array/drive-one

This copied everything on the external drive (should be 980GB). These files are now taking up 1.38TB on my new array.

So, could it have anything to do how I configured the sectors? Or perhaps the way I'm copying the files from my backup?


6*2TB RAID5 will give you between 8TB data and 4 TB parity and 10GB data and 2GB parity

The former gives you dual disk failure protection whereas the latter is discouraged as it gives you single disk failure protection without any further redundancy. Also, depending on the UI, you will see the real usage (including parity) or the fake usage (excluding parity), so what you're seeing doesn't look abnormal to me.

The ideal RAID5 set-up is 5 disks+1 hot-spare. The logic behind this being that you're buying all of the disks at the same time, so they will (probably) fail around the same time and if one of the disks fails, the hot spare takes over (that's why it's called "hot": it is powered on, but does nothing until one of the other disks fails) giving you time to order a new disk and continuing normal operations instead of "degraded mode" operations...

Now you can use the 6th disk not as a hot spare but as a hot drive giving you more parity, but you can also use it to increase storage and that one means sacrificing dual hard disk failure protection. and that is why it's discouraged... ;-)

Have a look at this RAID calculator here and play with the numbers for more information.

For more information: Wikipedia RAID explained (read it all, including the history) and a specific article on RAID5

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