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Replace Drive in RAID 5 Array

Posted on 2010-09-07
Medium Priority
Last Modified: 2013-11-14
I have a Dell PE2950 that has a Perc5i RAID controller that has 1 RAID 5 array on it with 3 drives.  I came to work today and one of the drives was in a degraded state (the orange and green lights were flashing.  My problem is that the system is out of warranty and I need to replace the drive.  The system will not boot to allow me to properly turn the drive off in Open Manage.  Can I simply take the drive out and put a new one in?  Will it be rebuilt by the other two good drives or will I lose my data on them as well?  Help is much appreciated.
Question by:marrj

Expert Comment

ID: 33617677
If you are feeling worried about the data on the drives, shut down the server pull the drives one by one and back them up with Norton Ghost or trerrabytes winimage on another machine that can read them.

Then just replace the drive with another one that is the same.

The RAID controller will rebuild it for you.

LVL 20

Expert Comment

ID: 33617726
Its odd that the system wont boot to allow you to investigate - even in degraded state all the data should be accessible, at least enough to boot. I would be concerned about moving the disks en mass to another machine - the raid config is generally stored on the disks and controller... moving a working set of disks to another machine is fine, doing so with one member that has failed can be a tad risky.

Swapping the disk will make the system start the rebuild process, it will detect a new disk and start automatically but i would really want a working backup first. Is there no way to force a boot... what is preventing you from doing so, this could indicate another base problem ?

Expert Comment

ID: 33617728
You should be able to remove the drive as it is hot swap. Replace with a new disk. Make sure it is a new unformatted disk. The PERC will do the rest.
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LVL 22

Expert Comment

ID: 33617736
You can replace the drive with a larger size if that is what you have.  If your original drive is for example 73GB size and you replace it with a 146GB drive it will work, you will lose the extra 73GB space though.
LVL 14

Expert Comment

ID: 33617797
You need to see why the array will not boot the OS before you attempt to rebuild this drive or replace it with another drive. When the server posts does it say 1LD Found, 1LD Degraded (or Failed)?
Boot the server to the BIOS Boot Menu - F11 and tell it to boot to the C:\ Perc 5i Controller, if you OS will not boot you have bigger issues than just a drive offline

Expert Comment

ID: 33618213
I agree the first thing you want to do is figure out why it wont boot into the OS.  The issue may or may not be related.

A RAID-5 volume has a minimum of three disks, and uses distributed parity to rebuild to a single replacement disk in the event of a failure.  In other words, you can lose one disk to hardware failure, and the RAID container has enough parity to rebuild the missing data from parity stored on the remaining two disk functional physical disks.

The PERC 5/i is an LSI based controller and is generally very good.
The blinking amber LED you have on the disk may however mean multiple things : Failed, Failure Predicted, Foreign, Rebuilding depending on the frequency of the blink and if there is any alternating green/amber sequences.

Reboot the server, and press Ctrl+R to enter the controller BIOS when you see it enumerate. "PowerEdge Expandable RAID Controller FW rev : xxxx"

Look for a Foreign View "Tab" at the top.
If there is one, then attempt to import the foreign configuration and reboot.
If there is not, check the PD "Tab" at the top. (Physical Disks)
You may have a failed disk, at which point replacing is necessary.

**Be aware that Data loss may be in play here, so hopefully you've got a full, valid, and tested backup.**
LVL 33

Expert Comment

ID: 33618355
Echo that ... go to CTRL-R and see what the status of your array is.  Check the status of each drive on the PD MGMT screen.
LVL 33

Expert Comment

ID: 33618378
Sorry ... not sure why my post was so slow going through :)

Expert Comment

ID: 33623262
Although, the boot loader files are distributed across the disks in RAID5 I don't think the boot sector is. Drive 0 in a RAID5 array always has to remain in first position in the array. Is drive 0 the failed drive?
LVL 33

Expert Comment

ID: 33623756
A good thought, but this is a something I've seen dozens of times and just isn't the case.  The OS on a PERC 5 RAID 5 will boot regardless of the drive that is removed/failed.

When you attempt to boot, where does it stop?  What error message are you encountering?

Accepted Solution

andr_gin earned 2000 total points
ID: 33625027
In a RAID5 array there can be one damaged disk and the system will continue:

1.) If one harddisk fails completely the system will still boot, but performance will decrease. If a working harddisk is detected and the harddisk is configured for that array the RAID5 will be rebuilt automatically. You can still work during the process, but the performance is reduced very much.

2.) If more than one harddisk fail completely the system will not boot any more and data will not be accessible any more.

3.) If one harddisk does not fail completely, but produces errors while writing instead the RAID5 does not help much, because there is no error correction. Maybe this the case in your situation. In this case you have to know which harddisk contains invalid data.

4.) If the controller fails RAID5 also does not help. If the controller produces only read errors you can replace it. If it produces write errors your data is corrupted.

5.) Keep in mind that nearly each controller has its own standard for saving data. You cannot exchange controllers without checking the upgrade path. If you make a backup with an image tool it will also be not so easy to recover the data without the physical controller.

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