RAID 5 Question

[Paddy]

I am in the process of setting up an ATA RAID 5 (4x300GB) array on an Adaptec 2400A.
I don't really want to buy all the disks at once. I'd rather buy them as I need them.

Is it possible to add a disk to an array and get it to incorporate the new drive without losing the data on the old ones? If so, I'd just buy the one disk, and then add others as it fills.


Cheers.

[schmosef]

I don't know the particulars of the 2400A but RAID 5 generally requires 3 drives to initially build an array.

From there, it's up to the features of the RAID controller whether it can incorporate new drives into the array later on. That feature that is pretty central to RAID 5 so most adapters should be able to do this. I'd expect that one from Adaptec would have this capability.

[Paddy]

yeah... but i can't really afford to buy three drives right now... so i'd like to just use one. I can use the drives seperatley until i have enough to make a RAID array... hmm... i'm not sure....

The one thing i know for sure, is that it will be a biatch trying to backup 600GB of data!

[schmosef]

If you're only using one drive, you don't need RAID. When you want to upgrade to RAID 5 you'll need to backup everything, build the array, probably do a minimal windows install on the new array, then restore your backup. If you're going to do this, you should install the RAID drivers now, even before you have a RAID array going, so that they'll be part of the backup/registry.

If you've got two drives to start with, I suppose you could setup a RAID 0 array...

[Paddy]

sorry, i am not making myself clear.
The array is for data storage only. There will be no OS installed.

The adaptor can hold four drives.
I plan to buy two drives now and create a RAID 1 array - the redundancy is a priority. When the first drive is full, I plan to buy two more drives. It should then be a simple case of erasing the redundant drive and creating a RAID 5 array whilst keeping the data on the first drive (I hope).

So now I buy two disks and have 300GB of storage.
When I run out of that, I buy two more disks and have 900GB of storage.

Is that clearer?

[schmosef]

Yeah that's clear.

In my experience, it won't work quite the way you want it to.

Creating the RAID 5 array will destroy all the existing data on each of the drives that join the array.

Your phase 1 idea is fine, but to move to phase 2 you'll need to back up all the data, build the RAID 5 array, then restore the data.

[Paddy]

crap

Unless I can create the RAID 5 array with the three disks and preserve one with data on it.
I can then copy the data onto the array and add the fourth disk to the set.

It's gonna be difficult to do it any other way....

[Sasq]

You will more then likely run into trouble on the single raid card, it will get upset about disk X not being attached, nor will it let you delete it - without killing the other - to use that port on the raid 5

[schmosef]

Actually, what you should do is this:

Phase 1) two drives iin mirror configuration
Phase 2) Buy two more drives, install one as none RAID. Copy RAID mirror to non RAID drive.
Phase 3) Break mirror and create RAID 5 array with first two drives and fourth drive.
Phase 4) Copy third drive data onto array. Wipe third drive and join array.

In theory, you could do without manually copying the data from the mirror to one of the other drives. That is, the data is already on each of the mirrors and all you have to do is select one of the drives as the source for copying the data onto the RAID 5 array. In practice, I've had problems with copying data off mirrored drives when one of the mirrors hasn't actually failed. I think it's something to do with the RAID controller marking the partition properly when it notices that one of the mirror drives has failed.

Your safest best is to manually copy the data to the third drive.

[Sasq]

just a thought... what OS will this be living on?
if its on a nix file server, you could always use software raid for raid1, and add the extra drives and controller card later...

non server Win os's I am fuzzy on regarding raid 1, as I have never bothered.

[Paddy]

would i be able to use a single disk from a raid 1 array in another computer? Or would it have to be connected the the controller in order for it to work?

[schmosef]

You will more then likely run into trouble on the single raid card, it will get upset about disk X not being attached, nor will it let you delete it - without killing the other - to use that port on the raid 5

Yeah, when you put the third drive in to copy the data from the array, install the drive to the motherboard's IDE controller, not the RAID controller. That's your safest bet because you don't want your RAID controller to suddenly get finicky and delete the mirror.

[schmosef]

would i be able to use a single disk from a raid 1 array in another computer? Or would it have to be connected the the controller in order for it to work?

As mentioned above, I've had problems with this. In theory it should work, but I've found that it only works when the RAID controller notices that one of the mirrors has failed.

[Paddy]

I'll mail adaptec and see if the controller can convert RAID 1 to RAID 5 by adding extra disks. I know that my SCSI controller can...

In any case, it will boil down to the cost of the drives.... Ican't find them for less than £118 here

[UtwigMU]

I'm not sure about dynamic expansion, you'll most likely have to do it by buying new drive, backing array to dvds or other drives and creating empty array from new drives.

3Ware 9000 series supports dynamic capacity expansion:
IE you have 3 160GB drives in RAID5:

you swap 1 drive for 300GB, rebuild array

repeat untill you swap all drives
then you can expand size of array.

You will need to use dynamic disks or Partition magic to expand array size.