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 Post subject: HA (Cage) availability
PostPosted: Mon Apr 07, 2014 3:23 am 

Joined: Tue Mar 04, 2014 11:12 am
Posts: 26
Hi All

Want to see what people think of HA Cage availlability?
Do you think its worth it?
I cant recall a customer ever losing a shelf, in any storage array. not just HP.

Dont get me wrong, most of our customer use HA cage avaialabiity.
I just want to see what people's thoughts were?


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 Post subject: Re: HA (Cage) availability
PostPosted: Mon Apr 07, 2014 5:30 am 

Joined: Sun Jul 29, 2012 9:30 am
Posts: 576
Being anal and paranoid I insist on cage HA, sure cage failures are very rare, but they can happen. We actually have an EVA right now with a bad slot in the shelf and need to replace the shelf. Total shelf/cage failures can happen, but like you said it is very rare. I like cage HA anyway because I know on the V400 it spreads the data across multiple cages thus spreading the IO over multiple FC paths.


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 08, 2014 12:52 pm 

Joined: Fri Feb 14, 2014 2:26 pm
Posts: 20
We do cage availability by default. HP's stance is that if you can do cage, then you do cage.

Now, on a 7200 with only two shelves, the only way I can do cage is by doing RAID 1, and then since we do RAID 6, we had to do magazine availability. Everything else though is all cage availability.

Seriously, scale your 3PAR where you can do cage availability so it just isn't something you have to worry about.


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 08, 2014 1:05 pm 
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Joined: Tue Aug 18, 2009 10:35 pm
Posts: 1143
Location: Ft Worth, Texas
In past experiences with EMC Clarrion cage replacements.... I will forever in the future opt for cage safe HA whenever and wherever possible.

_________________
Richard Siemers
Storage Admin, Pier 1 Imports
The opinions and positions expressed are my own and do not necessarily reflect those of Pier 1 Imports.


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 08, 2014 3:13 pm 

Joined: Tue Mar 04, 2014 11:12 am
Posts: 26
Good to see what peoples thoughts are, thanks for the replies.


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 08, 2014 5:49 pm 

Joined: Thu Oct 24, 2013 6:50 pm
Posts: 185
Dependant on your environment it may not cost anything (so you might as well use it).
For example, if you have two cages, and want to use RAID1, there's nothing to lose by configuring cage availability.

If you can only budget two cages, and want to use RAID5, well I don't think there's much of a question there.


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 15, 2014 2:30 pm 

Joined: Wed Mar 05, 2014 11:23 am
Posts: 13
So a question about cage HA. I have a 7200 with 4 shelves. All CPGs in use are RAID6. I see nothing in the UI that tells me I have cage HA. Does it automatically happen? How can you confirm that the array as configured provides cage HA?

Thanks...

-Andy


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 Post subject: Re: HA (Cage) availability
PostPosted: Tue Apr 15, 2014 2:47 pm 

Joined: Tue May 07, 2013 1:45 pm
Posts: 216
You have to check your CPG's availability setting, with 4 shelves if you're doing 6+2 RAID6 cage is an option.


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 Post subject: Re: HA (Cage) availability
PostPosted: Thu Apr 17, 2014 2:50 pm 

Joined: Wed Mar 05, 2014 11:23 am
Posts: 13
So in IMC I click on the CPG and then the Settings tab and see:

Availability
Requested cage
Current cage

So this means I should be able to loose an entire cage and not have data loss?

Thanks...

afidel wrote:
You have to check your CPG's availability setting, with 4 shelves if you're doing 6+2 RAID6 cage is an option.


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 Post subject: Re: HA (Cage) availability
PostPosted: Fri Apr 18, 2014 2:28 am 

Joined: Wed Aug 07, 2013 3:22 pm
Posts: 248
It's worth noting not all volumes have to be HA cage, you can vary between mag and HA using CPG's to gain greater efficiency for some volumes.

E.g

Production R5(3+1) has a 25% parity overhead
Development R5(7+1) would incur half the overhead but doesn't necessarily need the availability of HA cage, same for snapshot CPG's etc.

The point being you don't always need to think about cage as being system wide. if your workload doesn't warrant it, then you can save space by having lower parity overhead. CPG's are just policies so having them in place gives you flexibility, but costs nothing in terms of capacity.

When you're quoted usable capacity numbers with HA Cage that's the absolute worst case number. HA cage although free as a feature typically requires a small amount of additional investment in hardware which you need to factor in.

You should keep the above in mind when comparing usable capacity and cost with other arrays that aren't capable of guaranteeing HA Cage.


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