Combining Raid0 with Raid1

[mbonny]

Hello there!
I own a TS-451DeU with 4 disk slots QTS 5.0.
I have 2 disks of 3TB each in RAID 1 and a new empty 6TB disk.
As far as I know, the simplest option now is to make a RAID5 with 3 disks, but using only 3TB of the new one, with total capacity of N-1 = 6TB.
Is it possibile to create a RAID0 with the two 3TB disk, thus obtaining a 6TB raid group, and then create a RAID1 group using this and the new 6TB disk?
In other words
RAID1[ RAID0(disk1-3TB + disk2-3TB) ; disk3-6TB ] -> total capacity 6TB

I know that the capacity is the same, and a fault of any of the disk in raid0 will cause a need to change both of them, but adding in the future another 4th disk of 6TB:
1. in the first configuration I can create only a raid5 with 4 disks using only 3TB each: N-1 = 9TB (or a RAID6 N-2 = 6TB with 2 faults tolerance)
2. in the second configuration I can create a RAID5 with 3 "disks" of 6TB obtaining total N-1 = 12TB
I dont' see an option to downgrade from raid1 to raid0, so I think I have to start from the scratch.
Do you think this makes sense?
I know something similar is possibile with Linux, but I don't know if QTS allows it.
Thanks in advance to anybody that can help or suggest me.
Bye!

[dolbyman]

You could combine a RAID0 (3+3 TB) and a single disk (6TB) to a single pool with 12TB (~10.8TB)

https://www.qnap.com/en/how-to/tutorial ... management

Any change to this pool (failure of a single disk) will result in the total loss of the volume.

You can create a RAID5 Group (3+3+3TB) resulting in 6TB (~5.4TB) usable space with the 3TB of extra space on one disk wasted* and unusable with a single disk failure tolerance (if two fail, all data is gone)

* until you replace the other disks with 6 TB as well

Never forget full backups at all times (a RAID is never a backup)

[mbonny]

Thank you @dolbyman for your fast answer!
As far as I understand, what I was thinking to do is not possibile, but the only 2 viable possibilities are those you wrote.
I'm going to do a RAID5 group.
When I'll find another 6TB disk at an affordable price (I'm waiting for an offer), I'll evaluate if upgrading to RAID6 or add a spare drive to my RAID5: in this case, what you suggest?
Bye,

P.S. I have a backup of important data on an external USB drive that I swap periodically with another one located into another physical location, thanks for your suggestion

[dolbyman]

If you want to keep a spare, just keep it somewhere safe..dont stick it in the NAS

Also to upgrade/expand the RAID5 you would need two more 6TB drives, as the drive config is 3+3+6

[mbonny]

For backup I use external USB disks, I intend a spare disk following this sentence of the manual

In addition, if your system contains four disk drives, it is possible to use three drives to implement a RAID 5 data array with the fourth drive kept as a spare disk.

I can't add 2 more disks because I only have 4 bays: why I can't add just another 6TB and have a RAID5 with 3+3+6+6 ?
Am I forced to create a RAID6 in this configuration?
Thanks,

[dolbyman]

oh..so you wanted to add the drive not as a spare but as additional stripe..sure you could, but it would limit that 6TB drive still as a 3TB

So it would still be seen as 9TB (*0.9) storage

[FSC830]

To say it clearly: you need not to create a raid6 when using all 4 disks.
You can create (migrate) from raid1 to raid5 with 3x3x6TB = total 6TB capacity (the 6TB disk is used as 3TB disk)
You can add an additional disk to the raid5, ending in 3x3x6x6TB = total of 9TB (each 6TB disk used as 3TB)
You can create a raid6, ending in 3x3x6x6TB = total of 6 TB capacity (each 6TB disk used as 3TB)
Or you can have to raid1, 1st with 3x3TB, 2nd with 6x6TB in total 9TB in two raids.

Remember that at each disk some GB will lost.

Regards

[mbonny]

Thank you for showing me all the possibilities.
I don't know if it's better to have an additional stripe or to upgrade to a raid6, given that the space is the same, perhaps a RAID6 is more fail safe, but I can't downgrade to RAID5 if a 3TB old disk fails, which is the most probable scenario, and I'll have to buy a new disk.
I don't like the idea of doing 2 raid1 of different size (3+3 and 6+6), because I think that, in this way, I have to split the files in 2 different places with less flexibility.
Bye,

[dolbyman]

two raid1 can be pooled together ..so file handling would be done the same

but there is no space gain between 3+3 & 6+6 (Pooled RAID1s) VS 3+3+6+6 (RAID5) so stick with RAID5 and replace the 3TB down the road

Also have external backups at all times

[mbonny]

Thanks again dolbyman, I didn't know about pooling.
But if I do a RAID5 3+3+6+6 and one of old 3tb disk fails, can I maintain the Raid5 without replacing it, or instead replacing it is mandatory?
That's why I was thinking of using a 6tb disk as an additional spare stripe that can be used automatically by the NAS to substitute the broken one.

[dolbyman]

you always need to replace it as you fly without extra parity at that point (one more drive fails and the data is gone)

using spares on QNAP is a bad idea, as the spares spin with the disks (hidden system partitions) so the extra drive age without being used..so either keep a cold spare or expand your RAID to all 4 bays

[mbonny]

Very clear, thank you very much