Re: [somewhat OT] I just discovered that Stratis uses XFS.

[Eric Sandeen <sandeen@sandeen.net>]

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On 10/2/18 9:37 AM, Emmanuel Florac wrote:
> Le Tue, 2 Oct 2018 16:25:30 +0200
> Emmanuel Florac <eflorac@intellique.com> écrivait:
> 
>> Hi all, 
>> in fact I just discovered that Stratis exists :)
>> (https://stratis-storage.github.io/relnotes/relnotes-1.0.html)
>> ( details on https://lwn.net/Articles/755454/)
>>
>> Reading the FAQ (https://stratis-storage.github.io/FAQ.html) I see
>> that it uses XFS as a filesystem layer. Furthermore it seems to come
>> from RedHat. What are the relations with the future XFS capabilities
>> that Dave (IIRC) demonstrated recently?
>>
>> Sorry for the OT message :)
> 
> Oh, and what about the probable constant use of xfs_growfs? Stratis
> seems to create all filesystems with a size of 1TB, and extends them as
> needed from there. However that means that a filesystem could
> potentially be expanded many times, which, as I understand it, is very
> suboptimal or worse, can lead to problems (inode allocation, AGs
> count and structure, etc).

First, a disclaimer: I'm not a Stratis expert.

None of Dave's fancy new tricks are in Stratis, because right now Dave's
fancy new tricks are pretty much just in his lab.

As for the growfs, that's a little bit of a concern - in general, the "start
small and grow" worry is that we'll have a bazillion tiny AGs in the result.

But if Stratis starts at 1TB it's not terrible; I'd need to look and see how
many AGs get created (probably 4?) and if so, 250G AGs are not /too/ granular.
If it's creating a lot more smaller AGs, that could become an issue if it gets
grown to a very large size.  IOWs the growfs concern is mostly about the
resulting AG size & AG count.

-Eric


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