EX4100 RAID 1 to RAID 10 but not double space, why?

My Cloud OS 3 Personal & Network Attached Storage My Cloud EX Series
1

I had 2x6TB disks in a RAID1 with 5.5TB data. Then I bought 2 more disks and now I have 4x6TB disks.
I moved to RAID10 (12TB mirrored).
Then I put the data back on.

Now my WD says 35% available - how is that possible. It should be over 50% in my math.

Any explanations?

thanks.

2

Just some background for others that may be reading this thread:

RAID 10 is also known as “RAID1+0”.

In a RAID 10 setup, you have two pairs of disks.
Pair A is a RAID1 of two disks, 1 and 2. This means Disk 2 is a mirror of Disk 1.
Pair B is a RAID1 of two disks, 3 and 4. This means Disk 4 is a mirror of Disk 3.

Your RAID1+0 volume is a RAID0 array of and striped across Pair A and Pair B.

So a 4x6TB RAID10 will have almost exactly the same usable capacity as a 2x6TB RAID1.

So if your WD dashboard is saying that you went from an almost 95% utilized 2x6TB RAID 1 to 65% utilized RAID10, something ain’t right!

That sounds more like a 4x6TB RAID5.

I would suggest logging in via SSH and issuing the command

cat /proc/mdstat

…to get some insight as to what md thinks it’s doing.

3

thanks Tony,
I think a 4x6TB RAID5 would give me 18 TB of data space, so 5.5 TB data on
that would be something like 30%, while I would expect for a RAID10 of 12
TB that 5.5TB would be 45%.
In any case, a work colleague said that my data blocks might be rather big
and so if I have small files, it uses up more space than what is actually
required. I will look into this.
Thanks for the tip with the SSH command.

4

If you were at 95% of capacity on 2x6TB RAID1, you’d still be 95% on 4x6TB RAID10, right?

5

Not really,

if I have 2x6TB RAID1 that gives me 6TB for data (and 6TB for the
mirror). If I have 4x6TB in RAID10, then I get 12TB for data (spanned
over 2 disks) and another 12TB (spanned over 2 disks) to mirror those
two disks, so, my data only needs half of the 95% (of 6TB) = 48% (of 12TB).

Anyway, I found the problem. For some reason, when I tried to copy my
data back on the drive after upgrading to 4x6TB RAID10, the back-up
didn’t show that it had started in the Web Interface and I must have
tried to start it several times, which resulted in it copying many of
the files of my home videos on DVD up to 4 times, by adding a _1.vob,
_2.vob, etc. to the files, rather than overwriting them.

Now, I have deleted everything and reimported it successfully and, low
and behold, it is now at 47.5%:slight_smile:

Hope you have a great week-end,
Beat

7

Not sure this is correct.

  • A RAID 1 which consists of 2 x 6TB will give you a usable capacity of 6 TB (one disk is essentially a mirror of the other).
  • A RAID 0 which consists of 2 x 6TB will give you a usable capacity of 12 TB (No mirroring and data is striped across both disks.
  • A RAID 10 which consists of 4 x 6TB will give you a usable capacity of 12 TB. As Tony said each pair of disks makes up a RAID 1 set, so disks 1 and 2 will be “RAID Set 1” and disks 3 and 4 will be “RAID Set 2”. Each “RAID Set” as this point will be mirrored (RAID 1) and provides 6 TB of usable space. The two “RAID Sets” are then made into a stripe (RAID 0), resulting in 12 TB of usable space.

Cheers,

JediNite

8

What TonyPh12345 says is not correct. What JediNite says is correct.
And… in a 4x6TB RAID10 you can easily remove drives 2 and 4 and drives
1 and 3 keep working happily.
I keep disks 2 and 4 off site as a back-up (in case somebody breaks in
and walks off with the whole EX4100.
Once a week I bring them home and plug them in, it takes a couple hours
to rebuild and then I take them to out the next morning and keep them
off-site. This is not the original idea but it works perfectly.

Greetings,
Beat