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RAID 5 or NOT RAID 5?

Unlike other Micro Focus "Product Support" forums, this forum was created to encourage technical discussions whereby a variety of opinions and experiences can be explored and compared. This post is an attempt engage Community Members in such a discussion and determine whether other topics should be explored.

In recent years, there has been lots of controversy over whether or not RAID 5 is still an appropriate configuration. At issue is the long array rebuild time after a drive failure and the amount of data that must be read to recalculate parity. If an Unrecoverable Read Error (URE) occurs during the rebuild of the array, the rebuild cannot complete and all data in the array is lost. The larger the array, the greater the likelihood of encountering an URE.

As an example, if the specifications for the drives in the array state they have an Unrecoverable Read Error rate of one per 10E14 Bits Read, that would suggest there is better than a fifty percent chance that an URE will be encountered during the rebuild of a 12 TB array. Of course, the devil is in the details and the interpretation of the specs but would you trust your data to an array having these characteristics?

I'm not going to provide a lot of background at this time. A quick Google search will will provide you with many arguments both for and against. I hope, as this thread evolves, we can come to a consensus whether or not RAID 5 is still an appropriate configuration and, if so, under what conditions.

What are your RAID 5 experiences?

Are you concerned about the probably of encountering an URE during the rebuild of an array?
_____
Kevin Boyle - Knowledge Partner - Calgary, Alberta, Canada
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Re: RAID 5 or NOT RAID 5?

I think this is one of the big arguments for something like Ceph, which is
the basis for SUSE Enterprise Storage (SES) 4. Basically it works more
like eDirectory always has when it comes to redundancy by providing
multiple copies of everything, so a problem with one (of three, by
default) copy of the data means you have two more complete copies out
there. The downside is the big use of space (everything stored in
duplicate, or triplicate, or whatever) but you also have the ability to
provide much better protection of data by having a copy in this rack, and
that rack, and the datacenter across town, so that the chance of losing
them all is really low, where with RAID any big power outage, or network
outage, or hardware failure, could have everything offline. Add to that
the ability to use what kind of hardware (commodity disks) and cost
savings for big data storage are apparent.

I think RAID 5, 6, and 10 still have a place, and primarily in the tier
0/1 area where performance is paramount, and sizes are probably not in the
TiBs/PiB, maybe for rapidly-changing data (active databases) rather than
more-static data (media files).

--
Good luck.

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Re: RAID 5 or NOT RAID 5?

ab wrote:

> I think this is one of the big arguments for something like Ceph


That was to be my next discussion after we thrashed this one to death:
Storage Options.

I thought I'd start things off by discussing something with which most
visitors are already quite familiar.

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Kevin Boyle - Knowledge Partner
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Re: RAID 5 or NOT RAID 5?

ab wrote:

> I think RAID 5, 6, and 10 still have a place


RAID definitly still has a place. The issue is whether or not RAID 5 is
still an appropriate choice.

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Kevin Boyle - Knowledge Partner
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Re: RAID 5 or NOT RAID 5?

In article <KBOYLE.7sjoko@no-mx.forums.microfocus.com>, Kboyle wrote:
> What are your RAID 5 experiences?


I haven't lost any RAID5 systems, but did come close once when the RAID
definition got lost and needed a deep repair to bring it all back.
(Found backups had been silently failing, so recovery was really nail
biting)
I've been transitioning to RAID 10 with daily sync to another site for
most of my clients. They tend to be on the faster side and require few
drive Read/Write operations for a piece of data therefor reducing the
chance of an URE somewhat. Of course have been looking at fronting it
with SSDs to take things to the next level.


Andy of
http://KonecnyConsulting.ca in Toronto
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http://forums.novell.com/member.php/75037-konecnya
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Re: RAID 5 or NOT RAID 5?

konecnya;2449124 wrote:
I've been transitioning to RAID 10

That seems to be the configuration of choice these days.


They tend to be on the faster side and require few drive Read/Write operations for a piece of data therefor reducing the chance of an URE somewhat.

UREs are devistating if they occur during the rebuild of a RAID 5 array. If a drive fails in a RAID 10 array, it is rebuilt from the remaining good drive which does not require reading all the data on every drive in the array. URE's shouldn't be a problem.

Can you think of a situation today that might require a new pool of storage to be configured as RAID 5?
_____
Kevin Boyle - Knowledge Partner - Calgary, Alberta, Canada
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Re: RAID 5 or NOT RAID 5?

In article <KBOYLE.7slg00@no-mx.forums.microfocus.com>, Kboyle wrote:
> Can you think of a situation today that might require a new pool of
> storage to be configured as RAID 5?


Yup, really cheap customers


Andy of
http://KonecnyConsulting.ca in Toronto
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Re: RAID 5 or NOT RAID 5?

Andy Konecny wrote:
> Yup, really cheap customers


Economically conscious 🙂

- Anders


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Re: RAID 5 or NOT RAID 5?

In article <VA.00006edf.00925ec3@pedago.fi>, Anders Gustafsson wrote:
> > Yup, really cheap customers

>
> Economically conscious 🙂


Na, beyond that. Talking about so cheap here their
dollars/bitcoins/euros are more important than their data or time.
Cheap isn't always economically conscious, sometimes is just being a
tightwad (as in tightly clings to their wad of currency as their
'precious'). Just is hard to tell them apart at times.

Also starting with RAID 10 allows you on some systems to later shift to
RAID 5 to gain space to give you breathing space while initiating the
purchase of a new SAN (with new SAN install happening with one customer
this month)


Andy of
http://KonecnyConsulting.ca in Toronto
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Re: RAID 5 or NOT RAID 5?

Anders Gustafsson wrote:

> Andy Konecny wrote:
> > Yup, really cheap customers

>
> Economically conscious 🙂
>
> - Anders


There is a difference and one does get what s/he pays for.

It's easy to come to the wrong conclusion when one does not have all
the facts. And end users seldom have the same insight as does an IP Pro.

If a customer asks for a specific solution it's up to us to evaluate it
and advise the customer of the risks and any other shortcomings. If
they still insist on implementing *their* solution, we should either
document our concerns in writing then proceed or else walk away.

Years ago, RAID 5 was considered to be the best general purpose
redundant disk configuration. That is all that most people remember.
But things have changed:
- Storage capacities have increased dramatically
- Storage costs have decreased significantly
- Error rates have improved but not as dramatically as disk capacity.

As IT Pros it is up to us to explain to our customers that legacy
solutions may no longer be viable and that there may be better, more
cost effective ones available to them.

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Kevin Boyle - Knowledge Partner
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Kevin Boyle - Knowledge Partner - Calgary, Alberta, Canada
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Re: RAID 5 or NOT RAID 5?

Kevin Boyle wrote:
> As IT Pros it is up to us to explain to our customers that legacy
> solutions may no longer be viable and that there may be better, more
> cost effective ones available to them.


No arguments there.

- Anders


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Re: RAID 5 or NOT RAID 5?

KBOYLE;2448969 wrote:
In recent years, there has been lots of controversy over whether or not RAID 5 is still an appropriate configuration. At issue is the long array rebuild time after a drive failure and the amount of data that must be read to recalculate parity. If an Unrecoverable Read Error (URE) occurs during the rebuild of the array, the rebuild cannot complete and all data in the array is lost. The larger the array, the greater the likelihood of encountering an URE.


For those who may be interested, here is a link to a very good collection of in depth articles dealing with the advantages and disadvantages of various RAID configurations:
RAID Link Blast[/URL]

Enjoy!
_____
Kevin Boyle - Knowledge Partner - Calgary, Alberta, Canada
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