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Re: How to configure 36 disks ?

To: Raz <raziebe@xxxxxxxxx>, Bill Davidsen <davidsen@xxxxxxx>
Subject: Re: How to configure 36 disks ?
From: Jon Hardcastle <jd_hardcastle@xxxxxxxxx>
Date: Mon, 23 Mar 2009 09:02:14 -0700 (PDT)
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, Linux RAID Mailing List <linux-raid@xxxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx, linux-aio@xxxxxxxxx, "linux-ide@xxxxxxxxxxxxxxx" <linux-ide@xxxxxxxxxxxxxxx>
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In-reply-to: <49C7AC2C.9090307@xxxxxxx>
Reply-to: Jon@xxxxxxxxxxxxxxx
I'd like to understand how you even go attaching that many devices to a 
system.. I am 'comparatively' new to this.. and have a 6 raid5 system.. not 
enterprise.. and i have slammed into case/power/sat slot issues already. What 
sort of hardware must one use to grow to a 36 array system!

-----------------------
N: Jon Hardcastle
E: Jon@xxxxxxxxxxxxxxx
'..Be fearful when others are greedy, and be greedy when others are fearful.'
-----------------------


--- On Mon, 23/3/09, Bill Davidsen <davidsen@xxxxxxx> wrote:

> From: Bill Davidsen <davidsen@xxxxxxx>
> Subject: Re: How to configure 36 disks ?
> To: "Raz" <raziebe@xxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx, "Linux RAID Mailing List" 
> <linux-raid@xxxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx, linux-aio@xxxxxxxxx, 
> "linux-ide@xxxxxxxxxxxxxxx" <linux-ide@xxxxxxxxxxxxxxx>
> Date: Monday, 23 March, 2009, 3:35 PM
> Raz wrote:
> > Hello
> > I need to configure 3xDAS'es, each with 12 disks.
> > All three DAS'es are connected to a single
> machine.
> > I have the following requirements (in this order of
> importance)
> > from the storage:
> > 
> > 1. redundancy.
> >    having two disks failing in one raid5 breaks the
> entire raid. when
> > you have 30TB storage
> >    it is a disaster.
> > 
> > 2. performance.
> >    My code eliminates Linux raid5/6 write penalty. I
> managed to do by
> >    manipulating xfs and patching linux raid5 a bit.
> > 
> > 3. modularity ( a "grow" and it will be nice
> to have "shrink" )
> >    file system and volume must be able to grow.
> shrinking is possible
> > by unifying multiple file systems
> >    under unionfs or aufs.
> > 
> > 4. Utilize storage size.
> > 
> > I assume each disk is 1TB.
> > 
> >   
> ___ snip ___
> 
> > Any other ideas ?
> 
> Yes, you have the whole solution rotated 90 degrees.
> Consider your original solution #2 below... You have no
> redundancy if one whole DAS box fails, which is certainly a
> possible failure mode. If you put the RAID0 horizontally,
> two arrays size six in each DAS, then RAID6 vertically, if
> one DAS fails completely you still have a functioning
> system, and the failure results for individual drives
> remains about the same, while the rebuild time will be
> longer.
> 
> Solution #2
>                            raid0
> DAS1: raid6: D,D,D,D,D,D     |
>       raid6: D,D,D,D,D,D     |
>                             |
> DAS2: raid6: D,D,D,D,D,D     | xfs.
>       raid6: D,D,D,D,D,D     |
>                              |
> DAS3: raid6: D,D,D,D,D,D     |
>       raid6: D,D,D,D,D,D     |
> 
> 
> In addition, you can expand this configuration by adding
> more DAS units. This addresses several of your goals.
> 
> In practice, just to get faster rebuild as the array gets
> larger, I suspect you would find it was worth making the
> horizontal arrays RAID5 instead of RAID0, just to minimize
> time to full performance.
> 
> -- bill davidsen <davidsen@xxxxxxx>
>  CTO TMR Associates, Inc
> 
> "You are disgraced professional losers. And by the
> way, give us our money back."
>    - Representative Earl Pomeroy,  Democrat of North Dakota
> on the A.I.G. executives who were paid bonuses  after a
> federal bailout.
> 
> 
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