Constantine,
Just basically followup to say that I agree with you.
On 2016-02-15 17:41, Constantine A. Murenin wrote:
On 13 February 2016 at 08:50, Tinker <ti...@openmailbox.org> wrote:
Hi,
1)
http://www.openbsd.org/papers/asiabsdcon2010_softraid/softraid.pdf
page 3
"2.2 RAID 1" says that it reads "on a round-robin basis from all
active
chunks", i.e. read operations are spread evenly across disks.
Yes, that's still the case today:
..
There are presently no optimisations in-tree, but
the softraid policies are so simple that it's really easy to hack it up
to do
something else that you may want.
That is awesome.
Since then did anyone implement selective reading based on experienced
read
operation time, or a user-specified device read priority order?
That would make the code less readable! :-)
That is indeed an excellent reason for not adding an additional feature
- couldn't agree with you more.
Added complexity is (the root of all) 'evil'.
That would allow Softraid RAID1 based on 1 SSD mirror + 1 SSD mirror +
1 HDD
mirror, which would give the best combination of IO performance and
data
security OpenBSD would offer today.
Not sure what'd be the practical point of such a setup. Your writes
will still be limited by the slowest component, and IOPS specs are
vastly different between SSDs and HDDs. (And modern SSDs are no
longer considered nearly as unreliable as they once were.)
Yeah. I'm half-unwillingly starting to agree with that (discussed in
depth with Nick in the previous email).
2)
Also if there's a read/write failure (or excessive time consumption
for a
single operation, say 15 seconds), will Softraid RAID1 learn to take
the
broken disk out of use?
A failure in a softraid1 chunk will result in the chunk being taken
offline.
(What constitutes a failure is most likely outside of softraid's
control.)
My best understanding today is that Nick clarified this in the previous
post, that is, he clarified that softraid doesn't actually have any IO
operation timeouts, and IO lag will not lead to softraid plugging out a
disk - only a disconnect or specific disk failure SMART command from the
underlying disk will have that effect on softraid (of causing that
respective physical disk to be automatically disconnected).
..And therefore you need enterprise disks because they behave "cleanly",
as when using those only, essentially full softraid QoS is maintained at
all times.
Best regards,
Tinker
