11 replies to this topic

[dt225]

Hi all - first time poster but did search forums for an answer to this one first. Hope you can help!

I have a Highpoint Rocketraid 2340 card and am using 4x2tb in RAID 5 to store movies/music etc - gives me about 6tb of useable space.

Unbelievably, I'm running out of space and am considering investing in new 4tb drives to take the place of the 2tb ones. Unfortunately, space requirements mean I cannot simply add new drives and turn it into a 5 drive array - it has to stay as 4 drives max. Therefore, I want to remove one 2tb drive, put a 4tb one in its place, and let the array rebuild.

I have read that this might not be possible as the RAID will build based on the smallest capacity drive. Is this correct?

If it is possible, is there a precise process for removing one of the 2tb drives and then putting a 4tb drive in its place? - ie do I de-initialise that drive first, then physically remove it and replace it, then re-initialise the new drive and rebuild the array?

Finally - I am space limited so I understand the best practice might be to move all my data off first, then do this process. But I honestly dont have a spare 6tb sitting around to move my files onto!

Any help / guidance would be hugely appreciated.

Thanks.

David

[jmwills]

If this is a RAID 5, no. The drives must be of the same size if you want the array to be 4 x 4TB.

[pcdoc]

Drives have to be the same size and "should" be the same type. You start mixing and matching and we just might see a post on data recovery... . All joking aside, jmwills is correct, no can do. Your best bet is to look for some deals on some 3T and get 3 of them for now, then add the fourth when you need more space or get all four now.

[ikon]

Just to add to what the others have said, which is certainly correct, the type of 'RAID' that does what you want is Concatenation. It allows you to take drives of different sizes and link them together serially. The downside is that it has zero fault tolerance: i.e. if a drive fails you will lose at least everything on that one drive.

Also, if you wanted to implement Concatenation, it would require complete destruction of your existing array.

BTW, are you doing anything about backup, including offsite?

As an aside, I don't actually consider Concatenation to be truly a form of RAID, since it doesn't have any Redundancy: i.e. the R in RAID (I kinow, I know, neither does RAID 0, but that's another story). However, I think a lot of people treat Concatenation as a form of RAID because it is supported by many RAID cards.

[dt225]

Firstly, thank you for all of your responses.

By way of follow up, is one option to replace a 2tb with a 4tb, let it rebuild, accepting that only 2tb will be recognised, then repeat this 2 more times. Then remove the final outstanding 2tb, and let it rebuild around the 3 4tb drives? At the point where the 2tb is removed, the three 4tbs should be the only remaining drives. So, will the raid expnd to recognise the 4tb sizes?

Sounds unlikely and also I note the comment about re problems with installing drives with different sizes.

I do have offsite backup but this would, for a long list of reasons, not be the way to go.

As an aside, I was looking at Synology's hardware and they seem to be able to do the exact drive expansion method that I am interested. What do they have that allows this?

Thanks again!

David

[jmwills]

No. You will have an array of 3 x 2TB at that point. There is no way around this. You could, if one drive would hold it, copy the array over to a single drive, break the array and rebuid it with 3 x4TB drives, copy the data back over from the single drive and then add the 4th drive to the array.

[ikon]

You would, in the end, wind up with a 6TB array made up of 4TB drives, from what I know of most RAID cards on the market today.

Also, from what I've seen, all of the systems that can use different sized drives do it by some form of Concatenation. The difference with some of them is that they offer some form of redundancy. This is what Drive Extender did via software (Folder Replication), and some of its 'replacements' are doing the same thing in their own way.

[ImTheTypeOfGuy]

As an aside, I don't actually consider Concatenation to be truly a form of RAID

So glad to see you included this statement.

dt225,
there is no method that you can dream up that will do what you want to do. One option you could try, is to buy an external cage for an HDD and move the data from the current array and move the data to your 4 TB drives. With the remaining drives you could then begin building the array (since you are doing raid 5 with four drives you will have to copy data from one of the 4 TB drives to one of the 2 TB drives because raid 5 requires at least 3 drives to start. Yes this add complexity and time, but there is no other option.

[dt225]

All

Thanks for your replies and just resurrecting this for a moment. It appears that synology has a system called SHR where it is able to do precisely what I cannot do with RAID 5 - ie add new hard drives of varying sizes.

Has anyone used this system and/or has a comment on it?

Thanks.

David

[jmwills]

Yea, it's called WHS v1 with Drive Extender technology.

[ImTheTypeOfGuy]

Dave is using a synology so maybe he will see this post and reply.

Of course the drobo has that feature as well.

[ArchenRoot]

David,

I am going to buy this driver also. Have you already tried the 4TB drives? Unfortunately the manufacturer site is now down and I cannot find latest linux driver for 3.4-3.6 kernels, found only working patch for 3.2 kernel.

Thank you.

Ladislav