Gluster users - Nov 2016 - Improving IOPS

On Sat, Nov 5, 2016 at 6:20 AM, Gandalf Corvotempesta <
gandalf.corvotempesta at gmail.com> wrote:
> 2016-11-05 12:06 GMT+01:00 Lindsay Mathieson <lindsay.mathieson at
gmail.com
> >:
> > Yah, I get that. For me willing to risk loosing the entire gluster
node
> and
> > having to resync it, I see the odds as pretty low vs just losing one
> disk in
> > the RAID10 set and resilvering it locally.
>
> I don't see any advantage doing a single RAIDz10, only drawbacks.
> With multiple RAIDZ1 you get the same space, same features and same
> performances as a single RAIDZ10 but much more availability and safety
> for your data.
>
The only thing you gain with raidz1 I think is maybe more usable space.
Performance in general will not be as good, and whether the vdev is
mirrored or z1 neither can survive 2 drives failing.  In most cases the z10
will rebuild faster with less impact during rebuild. If you are already
using gluster 3 node replicate as VM practices suggest then you are already
pretty well protected if you lose the wrong 2 drives as well.

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Il 06/11/2016 03:37, David Gossage ha scritto:
> The only thing you gain with raidz1 I think is maybe more usable 
> space. Performance in general will not be as good, and whether the 
> vdev is mirrored or z1 neither can survive 2 drives failing.  In most 
> cases the z10 will rebuild faster with less impact during rebuild. If 
> you are already using gluster 3 node replicate as VM practices suggest 
> then you are already pretty well protected if you lose the wrong 2 
> drives as well.
Ok, i'll try again. I'm *not* talking about a single RAIDZ1 for the 
whole server.

Let's assume a 12 disks server. 4TB each. Raw space = 4TB*12 = 48TB

You can do one of the following:
1) *a single RAIDZ10*, using all disks, made up by 6 RAIDZ1 mirrors. 
usable space=4TB*6 = 24TB
2) *6 RAIDZ1 mirrors*. usable space=4TB*6 = 24TB

You'll get the same usable space for both solution.

Now you have gluster, so you have at least 2 more servers in
"identical"
configuration.

With solution 1, you can loose only 1 disk for each pair. If you loose 2 
disks from the same pair, you loose the whole RAIDZ10 and you have
to heal 24TB from the network.

With solution 2, you can loose the same number of disks, but if you 
loose 1 mirror at once, you only have to heal that mirror from the 
network, only 4TB.

* IOPS should be the same, as Gluster will 'aggragate' each pair in a 
single volume, like a RAID10 does, but you get much more speed during an 
healing.
* Resilvering time is the same, as ZFS has to resilver only the failed 
disk with both solutions.

What i'm saying is to skip the "RAID0" part and use gluster as 
aggragator. Is much more secure and faster to recover in case of 
multiple failures.
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