6 drives, 2x3tb 4x2tb, 3tb show as 2tb WTF

mdgm wrote:
I recently expanded my Ultra 6 volume. I had 6x1.5TB disks installed and I'm using X-RAID2 dual-redundancy. I had to install 4x3TB drives before expansion took place.

Thats an initial setup where you need the 4 disks to start RAID 6 with mdadm software. However this doesnt cover the expansion topic where you only need 3.

You will need to look at his logs when he adds a 3tb drive.

Md3 will be raid 6 with [UUU] - The raw disk space will be 1 TB extra

Each X represent 1 TB of raw disk space

XX
XXXXX
XXXXX

Currently here is what is going on (from here on out each X represents 1 TB of raw disk space and each O represents 1 TB of redundant space)

OO
OOXXXX
OOXXXX

[Raw disk space used (not including overhead and not including kilo to kibi conversions): 8TB and redundancy space will be: 3 TB]


The second he adds a third drive it will work

OOX
OOXXXXX
OOXXXXX

[Raw disk space used (not including overhead and not including kilo to kibi conversions): 11TB and redundancy space will be: 6 TB]

Although just having three 3TB disks will not give you RAID 6.

However in the setup of going from 3,3,2,2,2,2 to 3,3,3,2,2,2 I believe it will mdadm "cat /proc/mdstat" will say raid 6 and it will show you [UUU] and the extra TB will be used

Any how What it comes down to is this Add another 3 TB drive or add 2 more 3 TB drive. Lets see when it actually expands the volume using some of the extra md3 space (the extra space from the 3tb drives)

##############

I understand that if you start for example with

two disks X tb each and then add another X tb drive then it can be RAID 5 and then add another X tb disk it can become RAID 6.

Then if you add 3 disks of Y size. Y being X+a. You will be able to see the +a being used for volume after the 3rd disk

NOTE: () Parenthesis around the Redundancy

================================

(Y)XXXX raid 6

[Equals]

(a)
(X)XXXX

all the X portions make md2, the extra "a" from the Y disk makes md3, Ys extra "a" is wasted

================================

Same with the next setup

(YY)XXXX raid 6, both Ys extra double a are wasted

(aa)
(XX)XXXX

Both those "a" make the md3 but they cant be "raid6"ed yet by mdadm so its useless - in a way

================================

With next add ition mdadm will allow the dual redundancy to work

(aa)a
(YY)YXXXX raid 6

================================

This is from experience at looking through various setups like this

I will verify if im correct or wrong with L3 tommorow