topic Re: Replace Disk in RAID 5 with a previously used HD in HPE EVA Storage

Replace Disk in RAID 5 with a previously used HD

TonyJK1 — Tue, 05 Aug 2008 04:16:46 GMT

One of HD of a Compaq Server (RAID5) is broken. Instead of getting a new HD, my supervisor would like to replace it with another SCSI HD that has been used before.

From the web, we learn that we have to remove all data from the used HD before replacement. We would like to ask would it be a problem if we format the used disk as FAT and rebuild it with other 2 HD in the RAID 5 that is running NTFS ?

Moreover, we would like to know what is the best way to remove all data in a previously used HD. Is it necessary for us to break the RAID before doing so ? (The OS running on that server is not MS Windows).

Thanks

Re: Replace Disk in RAID 5 with a previously used HD

gregersenj — Tue, 05 Aug 2008 08:54:40 GMT

To delete the used disk, you can delete the metadata on the disk.

Install the disk in a server, with no other disks at all.
Hit F8, when prompted by the Smart Array controller.
Delete RAID, and it's gone.

However, and some may disagree with me.
What i would do:
1 .Ensure you have got a good backup. I always recommend this when messing with data.
2. Ensure that you got a fault tolerent RAID.
3. Hot remove, the failed disk.
4. Hot add, the disk you want to used.
5. Observe that rebuild starts - Look at the online LED (The middle LED) it should start flashing within a few seconds.
Flashing Online LED = rebuilding.
6. Observe rebuild has finished. Depending on HDD size, workload etc. It will take from 10 min - 1 day.

Note: Step 1 and 2 may scare you, but no matter how robust the Smart Array is, and it is rock solid, there is always a small risk. The risk apply for all disk systems.

I have rebuild on a used disk serveral times, and it has never failed (maybe it will someday).
Keep the server running.

Re: Replace Disk in RAID 5 with a previously used HD

Víctor Cespón — Tue, 05 Aug 2008 09:38:09 GMT

What controller does the server have?
You do not need to do anything special to the disk, just hot-plug it and the RAID controller will use it to rebuild the RAID.
The RAID controllers do not understand and do not care about filesystems.

Re: Replace Disk in RAID 5 with a previously used HD

TonyJK1 — Tue, 05 Aug 2008 10:18:42 GMT

The controller is a Smart Array 532 Controller. Unfortunately, the SCSI HD is not Hot Pluggable - A pretty old 36GB SCSI HD.

I would like to know
1) Existing unused Server
a) How to delete the meta-data of the existing used disk ?
b) For instance, if we boot up the existing unused server with a floppy disk and run fomart disk, does data in all 3 disks in the RAID are erased ?

2) Curuent using Server
a) How to identify which disk is broken (out of the three of the server in use) ?
b) We just find that it is Port 2 Drive 1

Thanks again

Re: Replace Disk in RAID 5 with a previously used HD

Víctor Cespón — Tue, 05 Aug 2008 10:30:37 GMT

If you have an server you can use for a while, put the disk in it, go to the Smart Array menu and Clear Configuration.
You can also boot with SmartStart CD and use ACU to do it. There's also an erase utility on the SmartStart CD, it will erase the disks and the BIOS settings on the server.

How to indentify the disk: If it's not hot-plug, it has no LEDs. What's connected to the Smart Array? A disk enclosure? If the disks are just on a SCSI cable, each one will have the jumpers on the back set in a different way, to assign a SCSI ID to each disk.

Re: Replace Disk in RAID 5 with a previously used HD

gregersenj — Tue, 05 Aug 2008 11:26:19 GMT

Agree.

How to erase disks.

Depending on how much you want to erase on the unsed server, here's the options:

1. If the unused server, also have got a generation 4,5 or 6 smart array.
Simply hit F8, when prompted by the Smart Array Controller.
Select Delete array.

-or-

2. Boot on at Smart start CD, Not newer than ver. 5.50 and not older than 5.0.
Now you have got 2 options:

2.1 Select Array configuration Utility, and delete array.

-or-

2.2 Select Erase Utility - Warning, Erase utility erases everything within a few seconds.

You do not need to format at all.

How to identify defective disk.
Since it's not hotplug, it must sit on a cable, wich means you must identify Disk 1, by looking on the jumper settings on the disks.
You can boot on a smart start CD, start Array Configuration Utility. It will tell you the setup of the array, and wich disk is failed. It will also tell wich SCSI ID.

Power off the server. Replace the bad disk.
Carefully follow on-screen instructions during post - Select rebuild.

Remove the Bad disk only!

Re: Replace Disk in RAID 5 with a previously used HD

TonyJK1 — Tue, 05 Aug 2008 23:10:39 GMT

Many thanks for both of you.

We don't have much experience in handling SCSI disk (Usually done by Service Engineer).

When we press F8 in the old server, we get the options for "Create / Delete / View Logical Drive".

We would like to confirm by selecting "Delete Logical Drive" will erase the meta-data of all SCSI HDs. Then we can reuse one of them to replace the broken HD.

Thanks

Re: Replace Disk in RAID 5 with a previously used HD

gregersenj — Wed, 06 Aug 2008 12:10:12 GMT

Yes.

If you only got the disk(s), that you want to delete, then just delete all arrays.

If you got more disk(s) than you want to delete.
Delete the array, wich the disk that you want to delete is a part of.
This will delete the array from all disk, within that array

I know, now i get it to sound complicated.
So here's a quick and dirty, i hop it will help you understand.

The smart array famely (SA), can be configured using 2 tools.
1. the ORCA, wich is what you do when you hit F8, during POST. You can do only simple arrays.
2. ACU, you need to boot and run it from the smart start CD, or run installed on the OS. - You can make advanced array setup.

a SA can have up to 4 SCSI channels (Model depending), and up to 14 disks on each channel.

If you got a lot of disks, you can create multible arrays.
And, if using ACU, you can create multible Logical units (LUN's), with different RAID levels.

A small excampel, to match your case.
Lets say you have got 6 disks SCSI ID 0 - 5.

On disk 0 and 1 You got array A, with 1 LUN - RAID 1 (Mirror)

Disk 2 and 3 - Array B, with 1 LUN - RAID 1

Disk 4 and 5 - Array C, with 1 LUN - RAID 1

This setup is possible to do with the ORCA.
During POST, the SA will tell you that it has found 3 Logical drives.

The information abaoute the array setup, and status, is stored on all the disks.
This is called meta data.
Meta data, also hold status, on failures, rebuild etc.
When ever you boot the server, the SA will read the meta data.

Lets say that you want to use disk 3 as a spare disk for another server, and Array B, is no longer needed.
You delete array B.
Meta data get deleted on disk 2 and 3, and array B, is removed in the meta data on the 4 other disks.
Now you got 2 "Empty" disks.
the Data on the disk is actually not deletet. But a SA will consider the disks as empty and unused.
If you have delete an array, you can't re-create it. The smart array do not have the functionality.
So if you by mistake delete the wrong array, it's create new array and restore from backup.

Lets take anothe example. 6 disks 3 arrays.
You have retired the server, kept the disks, disposed the server.
You take disk 3. Put it in a server, Disk 3 only. You power on the server, and the smart array read the meta data.
It will tell You, that array a is broken. array B is degraded. And array C is broken.
Broken = failed.
This is the meta data, saying this disk used to be a part of all of this.
You want to delete the meta data, in tjis senario you have to delete all 3 arrays.

I hope it will make you understand, and figure out what to do.

Re: Replace Disk in RAID 5 with a previously used HD

TonyJK1 — Thu, 07 Aug 2008 22:45:28 GMT

Many thanks for your advice. It is very helpful and comprehensive.

Re: Replace Disk in RAID 5 with a previously used HD

TonyJK1 — Thu, 07 Aug 2008 22:46:21 GMT

The advice is very helpful and I would like to close this thread.

Re: Replace Disk in RAID 5 with a previously used HD

gregersenj — Fri, 08 Aug 2008 06:43:47 GMT

Glad to help :)