Raid 5 newbie question

BarmyYeTTi · 13 May 2007 at 13:46

Im looking to take the jump to 3x 320Gb drives in Raid 5.

But I have a question regarding future upgrade of the raid...

basically, if in the future I wanted to upgrade to 3x 500gb drives would I...

a) have to start from scratch
b) could I replace one drive at a time rebuilding the array after each addition, and after replacing the final drive the array would use the full drive capacities of all the new drives.
c) another way

cheers

Netvyper · 13 May 2007 at 14:09

It all depends on the raid controller.

While changing the disks might be possible; its really not a pretty way of doing things, and im not sure i'd risk my data. You would have to re-build 3 times yes, and then do an online capacity expansion; to increase the available space/disk from 320->500.

If your buying a decent raid card; you could look at getting an 8 port card; at which point you could then add on 3x 500gb disks, move the data accross, and then have room for further expansion up to 8x 500gb.

That is assuming you already have the 3x 320gb, if you dont, i'd strongly reccomend going for 500gb disks, there isnt that much of a price difference, and it gives a reasonable degree of extra space/expansion.

rpstewart · 13 May 2007 at 15:00

I very much doubt that you'll be able to migrate a 3x320 array to a 3x500 one and access the extra space without nuking the array and starting again. If you replace one of the 320s with a 500 the controller will rebuild the array but only put 320Gb of data onto the new drive

As Netvyper says, get a decent 8 port card to give you not only some extra ports for expansion but also to get a decent XOR engine for parity calculations. Do not, whatever you do, use an onboard controller for a RAID5 array unless you have another separate disk to boot from and put the swapfile on. Onboard controllers don't have dedicated XOR engines and hence have very poor write performance.

elfy · 13 May 2007 at 15:20

what are some decent raid cards? any use PCI-E 1x?

BarmyYeTTi · 13 May 2007 at 15:31

thanks for the reply, and that was gonna be my next question elfy!

also... just been looking round and it seems my original idea of a SFF raid setup aint gonna work, so its gonna have to be a storage setup AND a SFF.

so another question is:
does the CPU and RAM make any difference to the RAID5?

I am looking at putting a reasonably beefy CPU, GFX card and lots of ram in the SFF, so looking to keep prices down on the Network storage system.

rpstewart · 13 May 2007 at 15:36

elfy said:
what are some decent raid cards? any use PCI-E 1x?

The only PCIe 1x RAID5 card I know of is the Highpoint RocketRaid 2300, it's only a 4 port card and the XOR engine is not a full hardware solution, instead it's an "accelerated software" card which still uses some of the main CPU for parity calculations. It's better than an onboard solution but not as good as a "proper" RAID5 card - it is a quarter of the price though.

If you want a high performance RAID5 card you need either a PCI-X slot or a free PCIe 16x slot to take something like an Adaptec 3085 or an Areca 1220 but expect to pay in excess of £300 for one.

BarmyYeTTi said:
does the CPU and RAM make any difference to the RAID5?

If the RAID controller needs any assistance (ie an onboard or Highpoint controller) then the CPU will have an effect on the write speed of the array. It you use a dedicated hardware card like the Adaptec mentioned above then the CPU doesn't matter.

BarmyYeTTi · 13 May 2007 at 15:43

thanks for that rpstewart... think my budget has just been exceeded!! bugger!

smids · 13 May 2007 at 17:00

Well, you could always pick up a decent SAS (Serial Attached SCSI) controller from an online auction. It is what I did and I've got a full hardware RAID5 card (Dell PERC5) which is 8 ports and supports SATA (as all SAS controllers do).

Surely, though, you could take an image using an imaging program like Acronis and simply restore that to the new drives....