Re: Metadata / Data on Heterogeneous Media

[Hugo Mills <hugo@carfax.org.uk>]

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On Thu, Feb 15, 2018 at 12:15:49PM -0500, Ellis H. Wilson III wrote:
> In discussing the performance of various metadata operations over
> the past few days I've had this idea in the back of my head, and
> wanted to see if anybody had already thought about it before
> (likely, I would guess).
> 
> It appears based on this page:
> https://btrfs.wiki.kernel.org/index.php/Btrfs_design
> that data and metadata in BTRFS are fairly well isolated from one
> another, particularly in the case of large files.  This appears
> reinforced by a recent comment from Qu ("...btrfs strictly
> split metadata and data usage...").
> 
> Yet, while there are plenty of options to RAID0/1/10/etc across
> generally homogeneous media types, there doesn't appear to be any
> functionality (at least that I can find) to segment different BTRFS
> internals to different types of devices.  E.G., place metadata trees
> and extent block groups on SSD, and data trees and extent block
> groups on HDD(s).
> 
> Is this something that has already been considered (and if so,
> implemented, which would make me extremely happy)?  Is it feasible
> it is hasn't been approached yet?  I admit my internal knowledge of
> BTRFS is fleeting, though I'm trying to work on that daily at this
> time, so forgive me if this is unapproachable for obvious
> architectural reasons.

   Well, it's been discussed, and I wrote up a theoretical framework
which should cover a wide range of use-cases:

https://www.spinics.net/lists/linux-btrfs/msg33916.html

   I never got round to implementing it, though -- I ran into issues
over storing the properties/metadata needed to configure it.

   Hugo.

-- 
Hugo Mills             | Dullest spy film ever: The Eastbourne Ultimatum
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                       The Thick of It

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