Le 21/12/2015 23:07, Steinmetz, Paul a écrit :
1) So the external DS8XXX gives a little more flexibility with the Raid Control, correct? You have the ability to change/stop Raid without IPLing the LPAR, correct?
I would not say the way you do.
The partition sees volumes which are somewhere a virtualization layer
provided by the DS of physical disks.
I wrote about the Protected vs Un-Protected status of a volume. This is
only a flag that the DS sends to the partition, so that you can activate
the mirroring at the ASP level. This was mandatory to use until IBM i
6.1, because in V5, the load source could not be member of a multipath
to volumes. You had to configure all the volumes as Protected so that
the microcode can establish a multipath to them using several fiber
chanel afapters, and two volumes as Un-Protected, so that the microcode
could create a mirroring for those two volumes to protect the load
source. Starting at 6.1, the load source can have several path, so all
volumes should now be configured as Protected. And again, this is the
case whatever the physical protection.
However, on the DS8xxxx, using a protection is mandatory. If you install
new physical disks, before we can use them to create volumes, you have
to start a protection over them. You cannot stop the Raid. Once the
disks protection is active, you can only change it to another way.
Formatting the disks to use a given Raid type require that they are not
allocated to any volume.
So, if you want to change the protection, you will have to perform the
way I will do for my partition (so that the physical disks are no longer
used by any partition), or do an unload/change protection/reload.
2) How much of performance hit do you think you took from external vs internal, I've been told internal are always faster.
The price/performance ratio is often better indeed for internal disks.
For instance, we are often configuring the protection to Raid10 (for
write intensive applications) which drives to an higher cost. Tools
exist to plan the needed configuration.
3) I need to revisit external storage options, prices, etc compared to internal.
The decision criteria will always depend on the expected usage and
performance.
In our case, we use external storage for all our (several tens ... and
more) partitions to provide great storage flexibility.We use them with
their great copy services (remote copye, flahs copy). And the
price/performance ratio can be competitive for us, in that context.
By the way, there are not only DS8xxxx on the market now, and more
competitive systems, like Storwize, exist.
Paul
midrange.com
