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From Erick Erickson <erickerick...@gmail.com>
Subject Re: SolrCloud recommended I/O RAID level
Date Thu, 01 Aug 2019 11:03:22 GMT
“why would I need a replication factor of 2….”

Two reasons:

1> assuming your replicas are located on different physical machines, you can lose one
and still keep on running. RAID won’t help if the machine dies.

2> capacity. Depending on your query load, having more than one replica distributes query
loads across multiple Solr instances, increasing the QPS you can handle.

If you don’t care about either of those issues, then no reason.

Best,
Erick

> On Aug 1, 2019, at 2:11 AM, Kaminski, Adi <Adi.Kaminski@verint.com> wrote:
> 
> Hi Shawn,
> Thanks for your reply, fully agree with your comments, it clarifies more the need of
RAID10 in this case.
> 
> One additional follow-up question - in case we follow this guidelines and having RAID10
(which leaves us with effective capacity of 50%), why would I need
> replication factor of 2 in our SolrCloud core/collection ? Won't it be double protection
layer, while the IO layer mirroring of RAID10 actually brings the value, and no need to copy
anything
> when we have IO failures ?
> 
> Thanks,
> Adi
> 
> -----Original Message-----
> From: Shawn Heisey <apache@elyograg.org>
> Sent: Tuesday, July 30, 2019 9:44 PM
> To: solr-user@lucene.apache.org
> Subject: Re: SolrCloud recommended I/O RAID level
> 
> On 7/30/2019 12:12 PM, Kaminski, Adi wrote:
>> Indeed RAID10 with both mirroring and striping should satisfy the
>> need, but per some benchmarks in the network there is still an impact
>> on write performance on it compared to RAID0 which is considered as
>> much better (attaching a table that summarizes different RAID levels
>> and their pros/cons and capacity ratio).
> 
> RAID10 offers the best combination of performance and reliability.
> RAID0 might beat it *slightly* on performance, but if ANY drive fails on RAID0, the entire
volume is lost.
> 
>> If we have ~200-320 shards spread by our 7 Solr node servers (part of
>> SolrCloud cluster) on single core/collection configured with
>> replication factor 2, shouldn't it supply applicative level redundancy
>> of indexed data ?
> 
> Yes, you could rely on Solr alone for data redundancy.  But if there's a drive failure,
do you REALLY want to be single-stranded for the time it takes to rebuild the entire server
and copy data?  That's what you would end up doing if you choose RAID0.
> 
> It is true that RAID1 or RAID10 means you have to buy double your usable capacity.  I
would argue that drives are cheap and will cost less than either downtime or sysadmin effort.
> 
> Thanks,
> Shawn
> 
> 
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