Riak on SAN

Jeremiah Peschka jeremiah.peschka at gmail.com
Wed Oct 2 18:02:20 EDT 2013


Responses inline.

TL;DR - I actually agree with John, SANs make management of storage
stupidly easy, but you pay more money for it. Make the right decision for
your org, but make sure you can monitor and backup that decision. The SAN
isn't a magic box. And  a Drobo b1200i [2] is definitely not a SAN.

---
Jeremiah Peschka - Founder, Brent Ozar Unlimited
MCITP: SQL Server 2008, MVP
Cloudera Certified Developer for Apache Hadoop


On Wed, Oct 2, 2013 at 2:12 PM, John E. Vincent <
lusis.org+riak-users at gmail.com> wrote:

> 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.
>

Agreed. You can buy a glorified direct attached storage device with a few
ethernet ports in it, but vendors will call it a SAN.


>
> 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.
>

We have the ability to cram 16x 960GB SSDs into the front of a Dell R720
for about $550 per drive... no SAN vendor can beat you on price for that.
SAN storage is an order of magnitude more expensive, but...


> 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.
>

The products worth of being called a SAN offer you fantastic features like
application aware volume snapshots, multi-site async and synchronous block
level synchronization, and all kinds of amazing features that mean you
never need to think about your storage beyond "HEY THERE, MAGIC BOX, I NEED
500GB OF SPACE!"


>
> 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.
>

For many applications, if you need storage performance outside of the main
chassis, you could also look at an approach like Microsoft take with the
Fast Track Data Warehouse Reference Architecture [1]. For those who don't
want to read, you line up the ability of your CPUs to process data with the
ability of your disks to produce data. For SQL Server, you assume ~300MB/s
of processing per core. Core count * 300MB/s = total combined disk speed.
It's easy to use something like a Dell MD1220 or an HP MSA to get this kind
of performance, too, without breaking the bank and upgrading to something
like a 3PAR or EMC.


[1]:
http://www.microsoft.com/en-us/sqlserver/solutions-technologies/data-warehousing/reference-architecture.aspx
[2]: http://www.droboworks.com/B1200i.asp?gclid=CPbhhL2T-bkCFeI-Mgod0hEAaA


>
>
>
> 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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