[pve-devel] [RFC PATCH 2/2] common: btrfs: lower minimum amount of disks for raid10 to 2

[Fabio Fantoni]

Il 15/01/2025 10:00, Daniel Kral ha scritto:
> On 1/13/25 13:24, Fabio Fantoni wrote:
>> btrfs profiles work differently but other hardware or software raids, 
>> many users may not inform themselves well beforehand but even in the 
>> case of informed users even if technically now btrfs allows lower 
>> limits with the creation of raid 0 (and raid10) I think it would be 
>> better to keep them at the base at the creation and then it must be 
>> the user who consciously makes any subsequent conversions.
>
> Hm, I'm still unsure about this, because AFAIK we already allow 
> creating ZFS RAID0 with a single disk, which technically also isn't a 
> "real" RAID0 setup itself. But fair point for RAID10, it could be 
> irritating for users to have a discrepancy between the minimum disk 
> amount of ZFS and BTRFS RAID10 and it'd be a bit harder to communicate 
> that in a understandable manner.

I'm not really sure if the difference with zfs (which they might not use 
at all by btrfs users) is more impactful, or at least how proxmox 
implements it, but I think it's more what you would expect in general 
and even if it recently allows the use of the raid0 profile in 
"fictitious" cases without requirements, or the possible removal of 
disks without needing to convert the profile, it still seems strange to 
me to have a "particular" situation by default, perhaps confusing even 
more any less expert users.

I could be wrong, it would be useful to have more people's opinions.

>
>>
>> regarding btrfs profiles at creation, one thing that could be useful 
>> is to always put duplicate metadata (dup with single disk or raid 1 
>> in the case of raid0), if you don't want it by default maybe put it 
>> as an additional option, and if you don't want that either at least 
>> add it to the documentation (as a suggestion if you want greater 
>> resilience of the filesystem without consuming excessive space)
>
> Currently, the installer creates the BTRFS filesystem with the data 
> and metadata both using the same profile. I also think it could be 
> valuable to have an "advanced" option, which allows to set a separate 
> profile for the metadata.
>
> Feel free to send either a RFC for it (even if I can't tell you 
> whether it will be accepted as it adds some complexity to the fs 
> setup) or create a Bugzilla so also other users and developers can 
> discuss it.
>
By default recently duplicate metadata is for all disk types, forcing 
them to single is a proxmox specific thing. so it seemed good to me to 
have at least the optional possibility to have them duplicated in the 
installation. eventually could at least inform about this thing in the 
documentation so that users are more aware and if they want they can 
convert the metadata profile easily and quickly (dup for single disk and 
raid1 in case of multiple disks in raid0).

regarding opening discussions I tried for some things even if there were 
few or no answers.
bugzilla seems to me little used, the forum is very much used and there 
is a minimum of participation but unfortunately given the enormous 
quantity of topics that are continuously created the topics quickly 
disappear from view.
I don't know what is best to do, eventually I will try to write again on 
the forum.


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