Re: XFS on top of LVM span in AWS. Stripe or are AG's good enough?

[Jeff Gibson <jgibson@xxxxxxxxxxxxxxx>]

Thanks for the great info guys.

Sorry to beat a dead horse here.  Just to be absolutely clear-

> > I guess what I'm trying to ask is - will XFS *indirectly* compensate
> > if one subvolume is busier?  For example, if writes to a "slow"
> > subvolume and resident AGs take longer to complete, will XFS tend to
> > prefer to use other less-busy AGs more often (with the exception of
> > locality) for writes?  What is the basic algorithm for determining
> > where new data is written?  In load-balancer terms, does it
> > round-robin, pick the least busy, etc?
> 
> xfs has no notion of fast vs slow regions.  See above for the basic
> algorithm; it's round-robin for new directories, keep inodes and blocks
> near their parent if possible.  
So if one EBS LVM subvolume has subpar performance it will basically slow down 
writes to the whole XFS volume.  XFS doesn't have any notion of a queue per AG 
or any other mechanism for compensating uneven performance of AGs.


> There are a few other smaller-granularity
> heuristics related to stripe geometry as well.
Oh, cool.  Since I'm considering stripe vs. linear for the LVM volume, I'd be 
very interested in what these are.


Thank you again,
JG