RAID1 vs RAID10

RAID1 vs RAID10

[Ulli Horlacher]

I have just discovered, that RAID1 is possible with more than 2 devices:

https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html#profiles

What is the difference to RAID10?

I have 4 x 3.8 TB SSD and want one filesystem.



-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
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70569 Stuttgart (Germany)      WWW:    https://www.tik.uni-stuttgart.de/
REF:<20251020122115.GA1461277@tik.uni-stuttgart.de>

Re: RAID1 vs RAID10

[Johannes Thumshirn]

On 10/20/25 2:21 PM, Ulli Horlacher wrote:
> I have just discovered, that RAID1 is possible with more than 2 devices:
>
> https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html#profiles
>
> What is the difference to RAID10?
>
> I have 4 x 3.8 TB SSD and want one filesystem.

For regular btrfs RAID, if you have more than 2 devices, btrfs will 
"decluster" the data on these devices (depending on how much free space 
is available). Then there is the multi copy RAID1 (RAID1C3 and RAID1C4) 
which will make 2 or 3 (depending on the level) copies of the data 
instead of 1.


RAID10 is the usual 4 (or more see above) drives, combine 2 into a 
stripe set and mirror inside the stripe set.


Hope that helps,

Johannes

Re: RAID1 vs RAID10

[Andrei Borzenkov]

On Mon, Oct 20, 2025 at 3:23 PM Ulli Horlacher
<framstag@rus.uni-stuttgart.de> wrote:
>
>
> I have just discovered, that RAID1 is possible with more than 2 devices:
>
> https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html#profiles
>
> What is the difference to RAID10?
>

In RAID1 each chunk (copy) is located on a single disk. In RAID10 each
chunk (copy) is striped across multiple disks.

https://lore.kernel.org/linux-btrfs/87v8qokryt.fsf@vps.thesusis.net/T/

Re: RAID1 vs RAID10

[Nicholas D Steeves]

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Andrei Borzenkov <arvidjaar@gmail.com> writes:

> On Mon, Oct 20, 2025 at 3:23 PM Ulli Horlacher
> <framstag@rus.uni-stuttgart.de> wrote:
>>
>>
>> I have just discovered, that RAID1 is possible with more than 2 devices:
>>
>> https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html#profiles
>>
>> What is the difference to RAID10?
>>
>
> In RAID1 each chunk (copy) is located on a single disk. In RAID10 each
> chunk (copy) is striped across multiple disks.
>
> https://lore.kernel.org/linux-btrfs/87v8qokryt.fsf@vps.thesusis.net/T/

Does the RAID10 profile still have equivalent read-speed to RAID1
profile on recent (>=6.12) kernels?  Last I looked into it both were
still limited to the speed of a single-device.

Regards,
Nicholas

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Re: RAID1 vs RAID10

[Andrei Borzenkov]

08.11.2025 05:10, Nicholas D Steeves wrote:
> Andrei Borzenkov <arvidjaar@gmail.com> writes:
> 
>> On Mon, Oct 20, 2025 at 3:23 PM Ulli Horlacher
>> <framstag@rus.uni-stuttgart.de> wrote:
>>>
>>>
>>> I have just discovered, that RAID1 is possible with more than 2 devices:
>>>
>>> https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html#profiles
>>>
>>> What is the difference to RAID10?
>>>
>>
>> In RAID1 each chunk (copy) is located on a single disk. In RAID10 each
>> chunk (copy) is striped across multiple disks.
>>
>> https://lore.kernel.org/linux-btrfs/87v8qokryt.fsf@vps.thesusis.net/T/
> 
> Does the RAID10 profile still have equivalent read-speed to RAID1
> profile on recent (>=6.12) kernels?  Last I looked into it both were
> still limited to the speed of a single-device.
> 

This is true for any single stream IO pattern unless it is using very 
large blocks.

To parallelize the single stream IO the stripe width (stripe element 
size, strip size) needs to be small enough. OTOH it will kill sequential 
IO.