Re: Asymmetric Disk I/O priorities in a RAIDframe RAID1?

[Greg Oster <oster%netbsd.org@localhost>]

On Mon, 28 May 2018 10:27:46 +0200
Hauke Fath <hf%spg.tu-darmstadt.de@localhost> wrote:

> All,
> 
> is there a way in RAIDframe to give a member of a RAID1 set read 
> priority, to e.g. favour reads from an SSD over rotating rust or
> iscsi?
> 
> The Linux mdadm(8) software raid config tool has the following option:
> 
> 
> "[...] devices listed in a --build, --create, or --add command will
> be flagged as 'write-mostly'. This is valid for RAID1 only and means
> that the 'md' driver will avoid reading from these devices if at all 
> possible. This can be useful if mirroring over a slow link."
> 
> 
> Can RAIDframe do anything similar?

No... RAIDframe basically selects the component with the shortest
queue.  If queue lengths are equal, then it tries to pick the component
where the data you want is 'nearest' to the last data item being
fetched in the queue (see rf_dagutils.c:rf_SelectMirrorDiskIdle()).

Later...

Greg Oster