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From Furkan KAMACI <furkankam...@gmail.com>
Subject Re: Pros and cons of using RAID or different RAIDS?
Date Sun, 21 Apr 2013 22:23:42 GMT
When I read documentation about Hbase it says RAID is not recommended for
many cases. When we talk about SolrCloud (and consider that if a machine
goes down there is a failure system via replicas) and when we think about
the purposes of different RAID disks:

do they true ->
using RAID systems for:

* *fault tolerance*: does not make sense because there is already a
mechanism at SolrCloud and instead of using my disks for such kind of RAID
purpose I can use that disk at somewhere else for a replica?

* *read and write performance:* I should select a RAID version for
considering about a good performance of read/write.

All in all maybe I should consider about Non-RAID drive architectures as
like JBOD?

What do you guys think about not considering RAID versions which has good
fault tolerance but considering read/write performance and maybe
considering about Non-RAID drive architectures?



2013/4/20 Shawn Heisey <solr@elyograg.org>

> On 4/20/2013 7:36 AM, Toke Eskildsen wrote:
> > Furkan KAMACI [furkankamaci@gmail.com]:
> >> Is there any documentation that explains pros and cons of using RAID or
> >> different RAIDS?
> >
> > There's plenty for RAID in general, but I do not know of any in-depth
> Solr-specific guides.
> >
> > For index updates, you want high bulk read- and write-speed. That makes
> the striped versions, such as RAID 5 & 6, poor choices for a heavily
> updated index.
> >
> > For searching you want low latency and high throughput for small random
> access reads. All the common RAIDs gives you higher throughput for those.
>
> The only RAID level I'm aware of that satisfies speed requirements for
> both indexing and queries is RAID10, striping across mirror sets.  The
> speed goes up with each pair of disks you add.  The only problem with
> RAID10 is that you lose half of your raw disk space, just like with
> RAID1.  This is the raid level that I use for my Solr servers.  I have
> six 1TB SATA drives, giving me a usable volume of 3TB.  I notice a
> significant disk speed increase compared to a server with single or
> mirrored disks.  It is faster on both random and contiguous reads.
>
> RAID 5 and 6 (striping with parity) don't lose as much disk space; one
> or two disks depending on which one you choose.  Read speed is very good
> with these levels, but unfortunately there is a penalty for writes due
> to the parity stripes, and that penalty can be quite severe.  If you
> have a caching RAID controller, the write penalty is mitigated for
> writes that fit in the cache (usually up to 1GB), but once you start
> writing continuously, the penalty comes back.
>
> In the event of a disk failure, all RAID levels will have lower
> performance during rebuild.  RAID10 will have no performance impact
> before you replace the disk, and will have a mild and short-lived
> performance impact while the rebuild is happening.  RAID5/6 has a major
> performance impact as soon as a disk fails, and an even higher
> performance impact during the rebuild, which can take a very long time.
>  Rebuilding a failed disk on a RAID6 volume that has 23 1TB disks is a
> process that takes about 24 hours, and I can say that from personal
> experience.
>
> Thanks,
> Shawn
>
>

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