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Does mirroring happens in consecutive logical drives for RAID 1+0

 
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Ranjith M
Advisor

Does mirroring happens in consecutive logical drives for RAID 1+0


I have a doubt rgd my above subject.
and what does the following mean
"Raid 1+0 disk failure from same pair is not supported"

Thanks and regards,

Ranjith
7 REPLIES
Steven E. Protter
Exalted Contributor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

Shalom,

What we need is some accurate information. What Linux distribution are you using?

What kind and model of hardware?

Are we trying to set up hardware raid or software raid?

A paragraph on what you are trying to do would be very helpful.

Basically, with the cryptic information provided it appears you are trying to set up raid in violation of rules, two raid sets on the same physical disk for example.

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Stuart Browne
Honored Contributor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

You have to understand the nature of the different raid levels.

Using any form of 1 and 0 can get very confusing as different people describe them differently, and unfortunately some are incorrect.

Going back to basics, you have the following:

RAID 0: Basic striping across multiple disks, no redundancy.

RAID 1: Mirroring across an even number of disks, able to survive the failure of a single member of each pair.

RAID 0+1 (01): Mirroring across striped sets of disks, can cope with a failure of multiple members of the same striped set.

RAID 1+0 (10): Striping across mirrored sets of even disks, can cope with a single failure in each mirrored set.

The best of the bunch is RAID10 as it is faster, and can cope with more failures.

(http://www.pcguide.com/ref/hdd/perf/raid/levels/ is a decent guide).

All this being said, I'd use LVM over a number of mirrored pairs for more flexibility.

Anyway, I have no idea what is giving you this error, bit I'd assume that a disk failed in one of the mirror sets that's been striped over, and for the entire set to remain consistent, it cannot cope with another disk failure from that mirrored set.

Replace the disk ASAP.
One long-haired git at your service...
skt_skt
Honored Contributor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0



RAID 0+1 (01): Mirroring across striped sets of disks, can cope with a failure of multiple members of the same striped set.

RAID 1+0 (10): Striping across mirrored sets of even disks, can cope with a single failure in each mirrored set.

As per the details given RAID 0+1 looks more redundant than 1+0 as it can support failures of multiple members.Both the ways the data is safe as they are mirrored.am i right?

if yes [.."and can cope with more failures."] your last statement about coping with the failurs looks contradictory.

Ranjith M
Advisor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

Iam really sorry for the confusion, if any.

My scenario is, i have 4 logical drives and trying to create a RAID 1+0. In this case first mirroring is done and then stripping rt? so does mirroring happens in consecutive logical drives or is there any option to specify the set(by user)?

Thanks and regards,

Ranjith
Patrick Terlisten
Honored Contributor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

Hello Ranjith,

do you try to build the RAID 1+0 with MD-Devices under linux?

If yes, you can specify which logical drive sbelong together. If you're using a Smart Array controller with four drives, building an array and a logical drive in this array with RAID level 1+0, you can't control which disks paired together. The controller will try his best, which means if disks are distributed over enclosures or cages, it will pair two disks together that doesn't belong to the same enclosure / cage.

You can try a third option: Build two RAID 1 with you RAID Controller and stripe them under linux.

Best regards,
Patrick
Best regards,
Patrick
skt_skt
Honored Contributor
Solution

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

"The controller will try his best, which means if disks are distributed over enclosures or cages, it will pair two disks together that doesn't belong to the same enclosure / cage"--Chances are lesser we to keep two storage enclosure, though it is very good for SPOF.

You can try a third option: Build two RAID 1 with you RAID Controller and stripe them under linux.
-->I don't recommend this option as this is something different than the standard RAID levels,though it looks logical, especially if this is meant for a production data.

Did any one has tried this option??Give some comments if any one else had implemented this way..
Patrick Terlisten
Honored Contributor

Re: Does mirroring happens in consecutive logical drives for RAID 1+0

Hello,

I use the third options sometimes to mirror logical drives betweeen storage-systems (host-based mirror), either for high availabilty (storage doesn't support controller -based mirror) or to copy data between two storages.

It was only an example, not a recommendation. :) If a RAID controller support RAID 1+0 there is no need to build single RAID 1 arrays and stripe them with linux.

Best regards,
Patrick
Best regards,
Patrick