Software mirroring overlayed on hardware raid 5.

Question

I have a new PE1800 with 6 146gig hard drives configured as raid 5 through a PERC4/DC.  That is way more space than I need and I am way more interested in fault tolerance than anything else at this point.  I was thinking of just creating a mirror from within the Microsoft Disk Administrator, splitting all that space into two mirrored volumes (although I can't quite wrap my mind around how that is going to work where the data is already striped across 6 drives)(I mean, how will that work if a drive goes out.  Will I be in any better shape than if I wouldve just left it at raid 5? it seems like I would not).  The Windows Server software is already installed and the raid 5 is configured so I don't know if I can change the hardware raid, or whether I can create a software mirror without losing any data.   Or, am I just wasting my time in that raid 5 has plenty of fault tolerance.  Mirroring appeals to me though.  Message Edited by Baddog24 on 09-29-2006 02:00 AM

Mark_A_Smith · Answer

It is always a bad idea to use dynamic disks on top of hardware raid.  Why not just reload the data?  You could recreate the array as a Raid 10 (striped mirrors)...

Mark_A_Smith · Answer

Yes.  It is bad for recovery purposes.  Software raid on top of hardware raid seems to cause recovery problems.

Baddog24 · Answer

Is it a bad idea because of performance issues, or recovery issues, or some other reason?   If I leave it as (hardware) raid 5 I still have fault tolerance as long as I lose no more than one drive in any situation, is that correct?

Dev Mgr · Answer

Why would you split a single virtual disk in 2 parts to then mirror them together?

It serves no purpose whatsoever;
- data corruption is mirrored to both halves
- if more than 1 drive fails, you lose both halves

I would agree that destroying the container and just creating a raid 10 is a much better option.

One thing with dynamic disk on top of hardware raid is that any little side effects with the hardware raid (drive failure may have some odd results on the partition/filesystem from time to time) are much more likely to have data-loss results than just using basic disk.

Baddog24 · Answer

On another machine (PE2800) I have two 73gig drives.  I think I set it up as raid 1 (mirroring).  To double check I went in to the bios utility for the PERC4/Di and it shows:   Raid Channel 0   ID-0  ONLIN A00-00 ID-1  ONLIN A00-01     Which I understand to mean both drives are in array 00.  So, I presume that I have it correctly set for mirroring, or am I missing something?   -------   Actually when I went into 'check data consistency' it shows up as one logical drive and says raid level 1.  So I think that one is right.    Message Edited by Baddog24 on 09-29-2006 03:18 PM

DELL-GaryS · Answer

Yes this is correct for a RAID 1.

PowerEdge HDD/SCSI/RAID

Software mirroring overlayed on hardware raid 5.

Was this post helpful?