Ahmadgmc
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RAID 10 on 8 disks (4+4)

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Hello,

I have some questions regarding RAID 10 and how does it work. your help is really appreciated

- The expression "RAID 1/0" does it mean RAID 10 or it may refer to another RAID level like RAID 1 ?

- The minimum number of disks for RAID 1 ? ( Two disks, please confirm)

- The minimum number of disks for RAID 1/0 ? ( Four disks, please confirm)

- Can i create a storage pool only contains 2 disks with RAID 1/0 when we use the Unisphere to create new storage pool?

-  RAID 1/0 has a preference of 4+4 disk but how data will distributed ove 8 disks , is it like the same distribution over 6 disks with additional RAID 1 set.

RAID10-6disks.JPG.jpg

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brettesinclair
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Re: RAID 10 on 8 disks (4+4)

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Yes, that's my understanding. It's the only way I've known R1/0 to be constructed.

Also, I recall a procedure referred to when I've created RAID 1/0 Groups in the past which showed the correct way to select the disks in order to determine the Primary & Secondary disks in each 'span'. ( There was no tertiary etc).

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brettesinclair
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Re: RAID 10 on 8 disks (4+4)

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Hello,

RAID 10 & 1/0 are the same

Minimum drive count for RAID 1 is 2. On VNX if you create a RAID 1/0 pool of only 2 disks, it really is only RAID 1 at that point as there is only a single mirror pair and thus no striping of pairs. It will not be displayed as RAID 1 though as expansion will then see mirror pairs get striped.

Minimum for actual RAID 1/0 is 4 disks, minimum recommended (for best practice) is 8 (4+4).

You can create a Storage Pool with only 2 disks, that will display as RAID 1/0 but will only really be RAID 1 unless it's expanded.

If you create a 4+4 RAID 1/0 I think the underlying disk groups will be 4 x (1+1) mirrors that will then be striped. In other parlance, each (1+1) group is a span.

Ahmadgmc
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Re: RAID 10 on 8 disks (4+4)

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thanks a million Brett.

So we can create a pool with two disks and if we choose RAID 1/0 the storage will treat these disks as a single mirror set.

in case we expand the pool by adding two additional disk , here the storage will treat the new set as a strip for the mirror set.however if the the first set is almost full, will the storage redistribute the data blocks over the four disks ( the old pair and the new one) or will it  write the new data on the new pair without touching the old pair.

I think you are talking about nested RAID, and what you described in your previous comment is RAID 100 . like the diagram below :

RAID_100.png

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brettesinclair
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Re: RAID 10 on 8 disks (4+4)

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Yes, when you expand a pool, the data is rebalanced/re-located across the existing and new disks.

and no, I wasn't referring to nested at all, that would require striping RAID 10 groups together, but maybe I didn't explain myself very well and have ammended it now.

The (4+4) notation seems a little confusing, but I expect the underlying construct is made up of  2 disk mirrors (1+1) that are then striped.

If EMC is different to other R1/0 implementations somehow, maybe someone can provide a reference.

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Ahmadgmc
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Re: RAID 10 on 8 disks (4+4)

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Sorry, I misunderstood what you said.

So can we consider a (4+4) RAID 1/0 as a 4 mirror pairs and the data blocks are stripping over these pairs.

  R1     R1    R1    R1

(1+1) (1+1) (1+1) (1+1)

I am asking about RAID 10 since I am little bit confused how blocks will be stored .

I really appreciate your help.

Thanks

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brettesinclair
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Re: RAID 10 on 8 disks (4+4)

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Yes, that's my understanding. It's the only way I've known R1/0 to be constructed.

Also, I recall a procedure referred to when I've created RAID 1/0 Groups in the past which showed the correct way to select the disks in order to determine the Primary & Secondary disks in each 'span'. ( There was no tertiary etc).

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Ahmadgmc
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Re: RAID 10 on 8 disks (4+4)

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thank you for sharing such information.

appreciate your help.

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kelleg
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Re: Re: RAID 10 on 8 disks (4+4)

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I've attached a couple of older documents, but the basics are still the same. In the Fundamentals starting page 69 is where the different raid types is covered.

TO determine the order in binding see the following KB  https://support.emc.com/kb/24160

glen