topic Re: Raid backups in Disk Enclosures

Raid backups

Jim Odom — Thu, 06 Feb 2003 19:52:41 GMT

My question is this. I have a 4 drive RAID 5 array. If I replace Drive 0 with a new drive...let it rebuild then proceed to replace drive 1...let it rebuild and finally replace drive 2 and let it rebuild. Will I have a good array with the drives that I removed? I was concerned if the parity rebuild would be intact across the three removed drives to allow it to rebuild the array if needed.

Re: Raid backups

Vincent Farrugia — Fri, 07 Feb 2003 09:40:20 GMT

Hello,

In theory that would work. To work, though, these steps must be obeyed:

1. Disk array is not in use (no writing is occurring).

2. Cache is disabled and flushed.

I understand that you want to backup your array using this method. It is not recommended, because:

1. You must have a large downtime to perform it (disk array should be unavailable for 3 rebuilds)

2. During rebuild, your data is unsafe, so if a disk fails during rebuild, you lose all data in LUN.

3. It is slow and clumsy.

The best way to backup your data is to use a good old tape drive. It is faster, and much safer this way.

HTH,
Vince

Re: Raid backups

e4services — Fri, 07 Feb 2003 12:03:59 GMT

I know that we have an HP document that describes this operation for replacing the drives with larger capacity drives, replacing each of your xGB drives one at a time with new xxxGB drives, rebuilding, until you rebuild the last drive and you will end up with a xGB logical drive and a (xxx-x)GB of free space that the OS will recognize and can be partitioned and formatted as usual.
I have experienced that the drives removed will be recognized as a viable drive if the are replace in the same order, same locations, a group for the array in the same order.

Re: Raid backups

Terri Harris — Mon, 10 Feb 2003 17:11:08 GMT

Vincent has included a lot of good information. My question is:

why do you want to do this?

Re: Raid backups

Roger_22 — Tue, 11 Feb 2003 03:39:13 GMT

This will definitely NOT work on a VA array!

A traditional (not virtualized) array might work, but do not write any data to the array during this process.

Re: Raid backups

Jim Odom — Tue, 11 Feb 2003 14:31:59 GMT

The reason we are doing this is this:
we are moving servers from one building to another. The data that resides is business critical. The app that runs creates thousands of 1kb tag files making it nearly impossible to backup with tape. So we were looking at backup/contingency plans for this move and that was one of the items brought up for investigation and as I have never done something like that with a RAID 5 array. I was wondering if it was possible. I mainly was unsure that when you rebuild an array does it use the same parity scheme each time or does it create a new one based on performance/usage data supplied by controller.

Thanks,

Jim

PS and of course we will stop all shares and manipulation of data while this rebuild process takes place.