Re: [RFC ONLY 3/8] btrfs: read raid-stripe-tree from disk

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 19/05/2022 13:48, Qu Wenruo wrote:
> 
> On 2022/5/19 19:44, Johannes Thumshirn wrote:
>> On 19/05/2022 12:37, Qu Wenruo wrote:
>>>> RAID1 on zoned only needs a stripe tree for data, not for meta-data/system,
>>>> so it will work and we can bootstrap from it.
>>>>
>>> That sounds good.
>>>
>>> And in that case, we don't need to put stripe tree into system chunks at
>>> all.
>>>
>>> So this method means, stripe tree is only useful for data.
>>> Although it's less elegant, it's much saner.
>> Yes and no. People still might want to use different metadata profiles than
>> RAID1.
> For RAID1 variants like RAID1C3/4, I guess we don't need stripe tree either?
> 
> What about DUP? If RAID1*/DUP/SINGLE all doesn't need stripe tree, I
> believe that's already a pretty good profile set for most zoned device
> users.
> 
> Personally speaking, it would be much simpler to avoid bothering the
> stripe tree for metadata.

I totally agree, but once you get past say 10 drives you might want to have
different encoding schemes and also have a higher level of redundancy for your 
metadata than just 4 copies.

The stripe tree will also hold any l2p information for erasure coded RAID 
arrays once that's done.

So this definitively should be considered.