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That's typically called
multi-datacenter replication. Beyond scope for RIAK, but a dilemma
for deployments all the same. Good point.
Some similar products (e.g. mongo) provide this but I think only
in their enterprise paid version or upper tier offerings.
On 10/02/2013 04:12 PM, Alexander Sicular wrote:
Cluster "redundancy" is no safeguard against the unknown. The only
true reliable protection is a complete offline backup in a
separate facility not run by the same provider as your primary
facility. I'm not saying everyone is running at that level of
paranoia, but it is something to consider against the value of
your data.
What if you get rooted and someone runs something like for
node in nodes rm -rf myriakdata ?
-Alexander Sicular
@siculars
Excuse me, if I misunderstood something, but
why you would even want to have backup of a single
node, if you are running 5 node cluster? Assuming
your W key value for put requests is higher then
number of vnodes on each physical node, scenario
when you loose data because of single node failure
does not seems to be possible. And restoring failed
node should not require data backup, as backend
hinted handoff should make all work for you and get
failed system back to state prior failure.
Sure, backup of initial state would be
helpful, as it would help to save plenty of time on
node re-setup, but redundancy on cluster-level seems
reliable enough.
I'm going to take a competing view here.
SAN is a bit overloaded of a term at this
point. Nothing precludes a SAN from being
performant or having SSDs. Yes the cost is
overkill for fiber but iSCSI is much more
realistic. Alternately you can even do ATAoE.
From a hardware perspective, if I have 5 pizza
boxes as riak nodes, I can only fit so many disks
in them. Meanwhile I can add another shelf to my
SAN and expand as needed. Additionally backup of a
SAN is MUCH easier than backup of a riak node
itself. It's a snapshot and you're done. Mind you
nothing precludes you from doing LVM snapshots in
the OS but you still need to get the data OFF that
system for it to be truly backed up.
I love riak and other distributed stores but
backing them up is NOT a solved problem. Walking
all keys, coordinating the take down of all your
nodes in a given order or whatever your strategy
is a serious pain point.
Using a SAN or local disk also doesn't excuse
you from watching I/O performance. With a SAN I
get multiple redundant paths to a block device and
I don't get that necessarily with local storage.
Could you do it? Sure.
Should you do it? No.
An advantage of Riak is that you can avoid the
cost of SAN storage by getting duplication at the
machine level rather than rely on your storage
vendor to provide it.
Running Riak on a SAN also exposes you to the SAN
becoming your bottleneck; you only have so many
fiber/iSCSI ports and a fixed number of disks. The
risk of storage contention is high, too, so you
can run into latency issues that are difficult to
diagnose without looking into both Riak as well as
the storage system.
Keeping cost in mind, too, SAN storage is about
10x the cost of consumer grade SSDs. Not to
mention feature licensing and support... The cost
comparison isn't favorable.
Please note: Even though your vendor calls it a
SAN, that doesn't mean it's a SAN.
Does this make sense?
--
Guy Morton
Web Development Manager
Brüel & Kjær EMS
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