topic Re: raid 0+1 in Disk Enclosures

raid 0+1

???_185 — Wed, 14 Dec 2005 19:36:37 GMT

is it same raid configuration betweeen 0+1 and 1+0?

Re: raid 0+1

Srinivasa_6 — Thu, 15 Dec 2005 00:50:13 GMT

Yep - they both mean the same (Striped Mirroring) and they might be used interchangeably.

Re: raid 0+1

Uwe Zessin — Thu, 15 Dec 2005 03:11:03 GMT

I don't recall if there is any standard that describes what is what (striped mirrors vs. mirrored stripes). I never use 0+1 or 1+0, but always talk about SM or MS to avoid confusion.

Re: raid 0+1

Srinivasa_6 — Thu, 15 Dec 2005 03:44:17 GMT

I stand corrected. In fact, there is a slight difference.

http://www.ofb.net/~jheiss/raid10/

Re: raid 0+1

DragomirAtea — Thu, 15 Dec 2005 05:11:24 GMT

Hi folks!

In my humble opinion there is a huge difference...

Mirrored stripes is dangerous to use!
They are infact two stripes that you mirror.

If you loose 1 diskdrive, the entire stripe will be lost, and youre running on a RAID 0. That means that you can only loose one disk in that configuration.

Stiped mirrors on the other hand, is multiple mirrors that you stripe. That means that you can loose 50% of your drives and still be up and running.

I would never set up a mirrored stripe in a working enviroment.

But..
Who says that I'm allways right, actually I was wrong once in 1976. (-;

Regards
Dragomir Zekic

Re: raid 0+1

John Kufrovich — Thu, 15 Dec 2005 09:18:35 GMT

Dragomir, your explanation is almost correct.

If you loose a drive from each set you loose access to your LUN.
With 0+1,
Drives 1 2 3 4
Set 1 = 0 0 0 0
Set 2 = 0 0 0 0

Set 1 is striped and Mirrored with Set 2. If you loose a drive in Set 1, say dr2. No problem you have set 2 for backup. BUT if you loose ANY drive in the Set 2. Then you have lost all access.

With 1+0
Drives 1 2 3 4
Set 1 = 0 0 0 0
Set 2 = 0 0 0 0

Each drive from each set is Mirrored with each other, then striped. SET 1 DR1 is Mirrored with SET 2 DR1. Then continue down the line. If we loose DR2 of set 1, no problem, we have the other drive2 as a mirror. The only time you could loose access if you lost drive2 of the Set 2. As Dragomir stated, you can loose 50% of your drives as long as the drive isn't the mirrored pair.

It is a matter of odds.
BTW, MSA and Smart Array Controllers do Raid 1+0.

Re: raid 0+1

Basil Vizgin — Sat, 28 Jan 2006 14:17:14 GMT

John,
how can I find what drives are in pair in raid 1 part of RAID1+0 array on SA (MSA) controllers?
If I split 1+0 array between 2 channels, are the members of pair on different channels?

This is important to understand how can array in MSA survive with enclosure failure.

Re: raid 0+1

Shameer.V.A — Sun, 29 Jan 2006 23:04:59 GMT

Hi zungwon ,
Please find the attached document. Hope this will help you to clarify..

Regards,

Shameer

Re: raid 0+1

John Kufrovich — Mon, 30 Jan 2006 09:54:14 GMT

Basil,

Take 6 drives, 3 from shelf A and 3 from shelf B. Disk A1 and B1 will be mirrored. A2 and B2, ...

Re: raid 0+1

Basil Vizgin — Mon, 30 Jan 2006 12:44:34 GMT

Thank you, John!

Re: raid 0+1

dipesh_2 — Tue, 31 Jan 2006 00:48:59 GMT

Hi

There is a slight difference.

RAID 0+1 configuration where multiple disks are striped together into sets (sets A & B in the diagram, each set being as large as the resulting final volume), and then two or more sets are mirrored together.

RAID 1+0 configuration where two or more drives are mirrored together (mirrors 1-4 in the diagram), and then the mirrors (as many as are needed to result in the desired amount of space) are striped together.

Re: raid 0+1

Sivakumar TS — Tue, 31 Jan 2006 01:12:08 GMT

Hi Zung,

DEFENETLY IT IS NOT SAME

Simply

raid 0+1 ==> striping the mirrored volume

raid 1+0 ==> mirroring the striped volume

the redundancy differs in both config.
the mirror can survive a single disk failure and stripe cant.

With Regards,

Siva

Re: raid 0+1

Uwe Zessin — Tue, 31 Jan 2006 01:20:51 GMT

dipesh and Siva have exactly opposite definitions.

That's why I said I always talk about striped/mirrors or mirrored/stripes ;-)

Re: raid 0+1

Basil Vizgin — Tue, 31 Jan 2006 17:28:30 GMT

From MSA CLI Guide:

Note: If more than one pair of drives are included in a RAID 1 array, the data is
striped across the first half of the drives in the array and then each drive is mirrored to a
drive in the remaining half of the drives for fault tolerance. This method is referred to as
RAID 1+0.

Re: raid 0+1

Adrian Parker — Thu, 02 Mar 2006 10:42:18 GMT

Hi,

Using the CLI to create a 1+0 lun, will the MSA 1000 automatically mirror across enclosures if it can, or is the lun set-up based on the order of disks on the command line ?

Thanks,
Adrian

Re: raid 0+1

Uwe Zessin — Thu, 02 Mar 2006 11:26:27 GMT

It's my understanding that the MSA controller firmware is "smart" enough to use different enclosures on its own. I believe somebody from the MSA team said so some time ago here on ITRC, but I am not sure I could find the thread easily.

Re: raid 0+1

Alzhy — Thu, 02 Mar 2006 16:16:51 GMT

ZungWon,

Peace!

1. 0+1 and 1+0 both gives you the same capacity

2. AS far as redundancy - 0+1 (stripe and mirror) will be able to handle more disk failures.

3. Performance - it depends on where the RAIDing is done. If RAIDing is done on the host level say - using VxVM, and you are dealing with JBOD enclosures - one RAID scheme may be better than the other performance wise.

Re: raid 0+1

John Kufrovich — Fri, 03 Mar 2006 09:27:56 GMT

Nelson,

Please recheck your second statement.

RAID 1+0 offers more redundancy than 0+1.

RAID 0+1 will only handle a single disk failure in each mirrored set.

Re: raid 0+1

Alzhy — Fri, 03 Mar 2006 09:36:19 GMT

John you are absolutely right. RAID10 indeed is more redundant.

Take 8 disks, carve 4 mirror sets (RAID1), stripe(RAID0) accross this 4 mirror sets and you've RAID10. You can loose 1 disk from each mirror set and your stripe stays intact.

In VxVM, you have what's called layered Volumes. You can have a stripe of stripes, s stripe or mirrors, a stripe of RAID5's, etc.. further incresing the reliability and scalability of storage.

Re: raid 0+1

Basil Vizgin — Fri, 03 Mar 2006 09:54:40 GMT

Both 1+0 and 0+1 can handle same quantity of disk failures (for instance, second disk can fail in already failed half of 0+1 mirrorset). But probability of array failure with subsequentd HDD errors is much different (1/2 in RAID0+1 vs. 1/number of mirrors in RAID1+0).