On 2014-01-21 01:42, Sandy McArthur wrote:
> On Mon, Jan 20, 2014 at 7:20 AM, Austin S Hemmelgarn
> <ahferro...@gmail.com> wrote:
>>
>> On 2014-01-16 14:23, Toggenburger Lukas wrote:
>>> 3. Improving subvolume handling regarding taking recursive snapshots (
>>> https://btrfs.wiki.kernel.org/index.php/Project_ideas#Take_recursive_snapshots
>>> ) and taking snapshots of arbitrary directories (
>>> https://btrfs.wiki.kernel.org/index.php/Project_ideas#Snapshot_arbitrary_directories
>>> )
>>
>> Another option that I would personally love to see would be support for
>> write-mostly devices (that is, devices in a RAID1/RAID10 setup that only
>> get written too unless the data can't be found elsewhere). This would
>> in particular provide an alternative to using bcache/dm-cache (namely an
>> SSD and HDD in RAID1 with the HDD set to write-mostly).
>> Based on the current development focus, I don't think anybody is working
>> on this already (I would be, but I don't have either the time or the
>> skills with kernel programming that would be needed).
>
> Maybe this happens already: Might a similar effect be automatically
> achieved by tracking per-device I/O load averages and distributing
> reads based on the I/O loads of possible read devices?
>
That might be the case, it depends on how the I/O load averages are
calculated. I actually hadn't realized BTRFS did this, I thought it
behaved more like MD RAID (that is, distributing the reads among devices
in a un-weighted round-robin fashion).
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