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thirteen_engines 09-17-2012 10:53 AM

Raid: Mixed drive sizes
I have had a question from the boss about mixed drive sizes in a raid system. I know next to nothing about raid so I thought I'd ask here.

We have a system that uses 160Gb drives but we can't get drives this size any more and I am wondering if we can use one or more 500Gb drives to replace any that fail. My understanding is that we can do this but that only 160Gb of the 500Gb drive will be used.

Also, if we end up replacing all of the 160Gb drives with 500Gb drives are we still stuck at 160Gb per drive or will it resize itself to the full 500Gb per drive?

Mark Pettit 09-17-2012 11:06 AM

Far as I my experience goes, you are correct that you can use a bigger disk in the array, but you will waste that capacity. Although if you add 2 or 3 drives that are "too big", you could in fact create a second array using just the extra capacity of the new drives.

As far as extending later when all the drives are replaced to the new bigger size (and assuming you haven't used the "spare" space), you should be able to extend the array, but it will depend on what you used to create the array in the first place (eg mdadm, hardware raid, proprietary ?).

/dev/random 09-17-2012 11:07 AM

Hi thirteen_engines,
You have the right idea, only 160GB of 500GB will be used, even if you replaced all the 160GB drives in the machine you will not get it to expand to 500GB automagically, depending if your raid device supports it, you would have to go into the raid setup utility and change the size of the array through its resize utility (if supported).

I cheap and dirty work around to this is to create a secondary array and move all the data off the first array then remove the first array completely then just add more 500GB drives in the place of the 160GB drives.(Most cards these days support online expansion).

EDIT: Mark Pettit beat me to it

jlinkels 09-17-2012 11:13 AM

The 500 GB disks today are probably cheaper than the 160 GB when you purchased those. Especially in a business environment the entire disk is probably worth less than 15 minutes of the hourly rate.

And yes, if you don't do anything special the remainder of the space is lost. If you were using mdadm you could utilize the remainder of the space by creating additional (non-raided) partitions. For other (hardware, proprietary) systems that might be different.

And the idea of creating a new larger-sized array and copy over the data is sound as well. Any data will grow beyond the available storage anyway. And if you do so, buy some spare disks right away. That will save you the next problem.


thirteen_engines 09-17-2012 11:42 AM

Thanks folks. This is pretty much what I thought would be the case. I didn't set up the system originally and as I said my experience with this is quite limited.

It looks like I'll probably end up setting up a second system and copying data over as you suggested. Seems the simplest approach.

Thanks again.

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