RAID 0+1 setup

Question

I noticed one of the configuration on the Dell web online. RAID 0+1 with HDD on Frontbay. How does the configuration works strip 2 hdd and then mirror again?Where does the O.S going to install on?

pcmeiners · Answer

Raid 0+1

It is a number of disks which are spanned, and then the spanned set is mirrored to an equal number of disks. You can lose 1 disk in the array, causing one of the spanned mirrors to fail, and the array remains , a second failure after this takes out the entire array. Basically the failure of 1 disk in a span kills the span involved, the mirror of the span can not take another disk failure. Under no circumstances do you want to create an array 0+1, it is just too dangerous ...an exceeding easily made mistake in an initial array setup.

This link explains the difference between raid 0+1 and 10

http://blogs.sun.com/roller/page/andresblog?anchor=raid_0_1_vs_raid

Raid 10 can handle 1 disk failure with no problem. If your a gambler, the odds favor raid10 especially in larger arrays. It is possible to lose a raid 10 with a second disk failure in any size array, but the favorable odds increase with the number of drives...

If a raid 10 array consists of 4 drives, drives 0 and 1 as mirrors 2 and 3 as mirrors.

If you lose drive 0, and then drive 2, your array is toast

If you lose drive 0 and any other drive your but drive 2, you survive a 2 drive failure..at best a 50-50 chance of failure with 4 drives, after 1 drive fails.

With say a 10 drive array, technically in the best scenario, you could lose 5 drives and still be OK, Murphy's law comes into being here, so never figure the best scenario, figure the worst, hotspares are important. The more drives you have in an array, the more you need a hotspares or a global hotspare, as the chances of multiple simultaneous disk failures increases with the number of disks, and with increasing numbers of blocks.

How to raid 10...

Slightly modified from the link below

From the raid bios console setup, CTL M on Perc adapters

Select CONFIGURATION / NEW CONFIGURATION
Select the first two drives for the RAID 10 array by pressing the spacebar twice, and ENTER once.
Select the next two drives for the RAID 10 array by pressing space twice, and ENTER twice.
Repeat this for the maximum number of drives you have for your array.
A summary screen displays the RAID 1 arrays. At the bottom for SPANNING, select YES.
Highlight ACCEPT and press ENTER twice
At the Save Configuration screen, select YES
Press a key to continue - Go to initialize drives. Select the drive to initialize, then press F10 to initialize. Initializing wipes all data from drives, and is necessary to make the logical drive usable.
After initialization completes, exit the utility and reboot. Background initialization on the newest adapters allows you to reboot immediately, and utilize the array for OS installation and data, though it is best to allow the initialization to complete before software installation.

http://lsionline2.lsil.com/esupport/esupportlsi/consumer/esupport.asp?id=cff7d451-f111-4eb1-9b19-de71291b4b9f&resource=&number=0&isExternal=0&nShowFacts=&nShowCause=&nShowChange=&nShowAddInfo=&activepage=statement.asp&bForceMatch=False&strCurrentSymptom=&searchtype=normal&searchclass=QuickSearch&bnewsession=false&selecttype=match

warwizard55 · Answer

Hi Jensen2,

Raid 0 plus 1 is dell's RAID 10 which has a raid 0 stripe layed across 2 or more raid 1's

The entire array is reported to the O/S as a single hard drive, just like any other hardware based RAID.

warwizard DCSP

PowerEdge HDD/SCSI/RAID

RAID 0+1 setup

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