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which raid 1 drive will rebuild after repartition of other drive?

Posted on 2009-04-03
Medium Priority
Last Modified: 2016-10-27
I'm thinking about the best way to repartition a raid1... and then got stuck.....

System details:
Dell Poweredge 2900 w/Perc5/i controller
--Raid 1: 67.75GB , two drives (0:1:0, 0:2:0)
--Dual Intel(R) Xeon(R) CPU X5355 @ 2.66GHz  
--16384 MB RAM
--Microsoft Windows Server 2003 R2, Standard x64 Edition  Version 5.2 (Build 3790 : Service Pack 2) (x64)

here's the scenario i've brewed up:
1. I turn the server off
2. I pull drive 0:1:0
3. Power server on
4. Quickly use a boot disc like acronis disk director or g-parted
5. Repartition 0:2:0 (giving more space to the C drive)
6. Reboot computer
7. Five minutes later plug 0:1:0 back in

my question is will 0:1:0 rebuild to be exactly like 0:2:0 ?  Is this the safest way to repartition a raid 1?

Question by:braker15
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LVL 18

Expert Comment

ID: 24063880
Those "repartition" tools may render your disk unusable so you should extensively test (not "5 minutes later" please) your drive 0:2:0 BEFORE rebuilding the array :
-copying some folders to nul:
-opening some files

I don't think 0:1:0 will come back without some manual opérations like rebuilding the mirror from the Perc 5i tools (at Bios startup).
LVL 47

Expert Comment

ID: 24064371
I am curious to know why do you take out the drive? As far as I could understand your primary goal is to resize existing configuration so to give more space to C: drive and for this purpose you want to take a drive from from RAID?
There is more simple way to do this using partitioning tool in Windows. I have less experience with Acronis Disk Director or GParted thus going to give example based on Partition Manager tool produced by Paragon: www.partition-manager.com
Lets say you have C: and D: drives where vendor partitioned 12GB to C: and 120GB to D: drive and now C: is getting full. Install Partition Manager - run it - right click on D: - catch the left border of partition and drag to to right taking free space block for C: drive. Then apply changes and wait till it completes the work.
Then right click on C: - move\resize - catch the right border of drive and drag it to right so allocating space to it. Apply changes and in 1-2 minutes your resize is done.
Hesitation about data safety? Use inbuilt ghosting feature to take backup of entire drive (RAID) to network or external drive.

Author Comment

ID: 24065063
i take out the drive because if the repartitioning makes the drive 0:1:0 unbootable, i don't want 0:2:0 unbootable too...  (instead i'd just pop in 0:2:0 and rebuild the raid 1 back to its original working state)

I'm hesitant about any image, especially raid images.  I want to always have a working copy of the original setup on an extra drive.

I guess what i really want to do is have an extra hard drive 0:3:0 be an exact copy of 0:1:0 and 0:2:0 before starting this whole process.. that way.. worst case scenario if drive 0:1:0 doesn't repartition properly and drive 0:2:0 physically dies i'm not screwed (this is a really important server).

The only problem is i don't have an extra bay.  I'm going to check out the PERC 5i config utility in post tomorrow and see if i can make a copy of 0:1:0 to 0:3:0... then i'll image the drives separately and compare them byte by btye ...... this probably sounds insane but  like i said it is a really important server (or i could just be extremely paranoid because i've never taken an image of a raid before)
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LVL 56

Expert Comment

ID: 24067670
If you boot with one drive missing then replace it the controller is going to know which drive it is currently using so won't overwrite the wrong one.
LVL 47

Expert Comment

ID: 24068306
Hardware RAID is detected by Windows as single HDD if correctly configured. This virtual HDD can be imaged by software utilities like Ghost (Paragon, Acronis etc). So there is the insurance that you could restore to the working state from image if anything goes wrong. Resize on production server is a common task for me and using the procedure I recommended you will handle the task easily.
Take backup image and then resize it. No hard drive disconnection is needed as it could cause more problems than you do expect.

Author Comment

ID: 24068610

if i boot with one drive missing... whn should i add the second drive (that i want to mirror the boot drive)?  at some point during post? after i am in windows?


also.. maybe i should convert disc image to virtual machine to be sure it is good

Expert Comment

ID: 24068647
First off, a RAID1 is not a disaster recovery solution.  I would highly suggest that you use a software type backup program that does incrimental backups.  I prefer Acronis.

Secondly, I really think you should consider what you are doing entirely.  This sounds extremely risky, and it is highly unconventional.

Third, to actually help you with the question rather than try and tell you how you're doing everything wrong... LOL.  I would suggest that you image the drives when the system is booted up.  Then, I would simply save that image on a completely separate drive.

You see, acronis does not take the actual RAID into consideration when it is imaging.  It looks at the actual data that is located on the virtual drive.  That said, If you back up each virtual drive with Acronis, you should have no problem loading everything back after you have created your new partitions.  So, again, Acronis will not be imaging your RAID configuration.

HOWEVER:  If you should feel worried that you will have an issue regarding the RAID, I would higly suggest getting Acronis Universal Restore.  It will give you a 99.999% guarntee that your plan will work.
LVL 47

Expert Comment

ID: 24069038
hmmm, why make things so complicated? And how does Acronis differ from solution suggested by me? All of these backup solutions like Acronis, Paragon or Ghost are taking sector level images and there almost no difference between these products. I think Baker needs the cheapest way out and most reliable one.
Braker, kick off your worries, take backup image of the system as insurance and resize your configuration using steps suggested in my first step.

Expert Comment

ID: 24073825
So to answer your question its just a matter of simple logic.

RAID 1 is an exact mirror.  

Now that's not the absolute safest way to do it, but for knowledge sake here is the answer to your question.  You pulling drive 1 out of your RAID array is essentially creating a drive failure, so when you re-insert the drive you pulled to begin with, you're basically replacing a failed drive.  The RAID set is going to assume that new drive you just put in, whether you have data on it or not; is a new drive and will rebuild from the old drive, onto the new drive.

So yes, you can pull the drive 1, repartition drive 2, re-insert drive 1, and it will rebuild off of drive 2.

Just keep this in mind, a RAID controller is not intelligent and does not look at what kind of data is on the drive, what partitions are bootable or anything of that sort - and simply makes a dumb copy.  So if errors occur, the chances of it being the RAID controller are very slim.  Just make sure you have drive 2 exactly how you want it, check that it boots after using something like gparted, partitionmagic, etc.  Then recreate the mirror.

Hope this helps.
LVL 18

Accepted Solution

BigSchmuh earned 2000 total points
ID: 24075192
Your very first scenario is the good one !

Just take time to test your 0:2:0 drive instead of taking back the 0:1:0 one "5 minutes later".

NB: Having a normal backup is good point too...but I guess you already have one.

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