Raid 5 storage calculation

[Reemster]

Hello,

I have a 'problem' with raid 5.. At the moment i have 2 disk 8TB inside, and 1, 4TB disk. But the total amount of space is at the moment 7TB... WTF?

I don't have experience with a Raid 5 configuration, and the NAS is still busy with syncen and building EXT4 ... so maybe i get more space when it's finished ? or stay it with 7TB?

Sorry for my n00b question

Gr,
Remy

[Nazar78]

Seems fine, the array (striping + distributed parity) will use the smallest disk/partition size available for all disks. For your case 8+8+4 = 4+4+(4) = 8, last figure (4) is allocation for parity and after taking account the file system, total size is around 7TB.

Suggest you learn more about RAID specifically for your level 5 array here https://en.m.wikipedia.org/wiki/Standar ... els#RAID_5

[Reemster]

I have read some stuff about it of course. But what ive read a raid 5 configuration takes normally 10/15% of space with the total amount? (probably i read this wrong) it's so weird that as it turns out, it use 13TB of space from the 20TB total, to 'protect' 7TB of data, so that's not gonna work for me

But thanks for your reply

[Nazar78]

The percentage depends on the number of disks, your case 3 disks will incur 33.3%. That 33.3% is always the size of one disk allocated for parity data. More disks equals more usable space.

But that's only half of your issue, the other half is you're using a smaller one 4TB disk which will result to all the array size to reduce to 4TB each disks.

To fix this, swap the 4TB to 8TB, use the Storage Wizard to expand then resize. If you have no data, you can quickly delete the RAID 5 then redo. You will then have 8+8+(8~parity) = 16, approximately 15TB of usable space.