On 02/15/2018 02:11 PM, Hugo Mills wrote:
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.
Very interesting thread. Thank you for sharing Hugo. That nomenclature
is rather expressive, and the design covers a much broader base than I
was imagining.
Best,
ellis
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