Riak on SAN

Victor Victor at boirefillergroup.com
Wed Oct 2 16:03:12 EDT 2013

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. 


From: riak-users [mailto:riak-users-bounces at lists.basho.com] On Behalf Of John E. Vincent
Sent: Wednesday, October 02, 2013 3:12 PM
To: riak-users
Subject: Re: Riak on SAN


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. 


Just my two bits.



On Wed, Oct 2, 2013 at 2:18 AM, Jeremiah Peschka <jeremiah.peschka at gmail.com> wrote:

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.

On Oct 1, 2013 11:08 PM, "Guy Morton" <Guy.Morton at bksv.com> wrote:

Does this make sense?

Guy Morton
Web Development Manager
Brüel & Kjær EMS

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