Software RAID-1 with two different drives

justdanyul · 2013-08-12 10:34:47

Hi,

I got a 2 TB Seagate Barracuda, which I am looking to mirror in a RAID-1 set-up. Now, since the space is filling rather fast, I suspect I'll have to keep adding disks to this machine in the future. So, I have a interest in changing to some low power (since its always on) drives.

So, I'm thinking of making the second disk a 2 TB Seagate NAS drive (and then use NAS drives from this point on), which is a fair bit slower than the main drive. Personally, I wouldn't expect this to be a problem at all, but I thought it would be best to check with others first though

Have anybody here tried running a RAID-1 where one disk is considerably slower than the other? Will this give any issues (other than the speed being limited by the slower disk)?

cellisten · 2013-08-12 14:18:11

Have you thought about using btrfs instead? That would make it a lot easier to extend the RAID setup...

WonderWoofy · 2013-08-12 14:34:25

The speed will certainly be limited by the slowest device, as you mentioned, but what I am confused about is what you expect to achieve by continually adding drives to a RAID-1? At some point, do you plan on changing the RAID level? Because RAID-1 is mirroring. If you add another drive, you will not get more space, you will just get another copy of your data... and another... and another.

I'm not sure that btrfs would be any easier in this case, as the mdadm tools are pretty robust and certainly allow for adding and removing drives. But if you use btrfs it might actually be beneficial if you are set on keeping a RAID-1 type setup. This is because btrfs' raid levels are not quite like traditional raid. If you put your btrfs array in a RAID-1 setup with two disks, it is no different. But when you add another disk, it will continue to keep just two copies. So if you have a total of four disks, then it will still be only two copies of any given data, meaning that you will end up with twice the space of the two disk RAID-1.

Maybe you are thinking of a different RAID level altogether? If speed is not the issue but you care about redundancy and fault tolerance, then you might want to look into RAID-5 or RAID-6, though these require quite a few disks.

justdanyul · 2013-08-13 12:35:29

WonderWoofy wrote:

The speed will certainly be limited by the slowest device, as you mentioned, but what I am confused about is what you expect to achieve by continually adding drives to a RAID-1? At some point, do you plan on changing the RAID level? Because RAID-1 is mirroring. If you add another drive, you will not get more space, you will just get another copy of your data... and another... and another.
I'm not sure that btrfs would be any easier in this case, as the mdadm tools are pretty robust and certainly allow for adding and removing drives. But if you use btrfs it might actually be beneficial if you are set on keeping a RAID-1 type setup. This is because btrfs' raid levels are not quite like traditional raid. If you put your btrfs array in a RAID-1 setup with two disks, it is no different. But when you add another disk, it will continue to keep just two copies. So if you have a total of four disks, then it will still be only two copies of any given data, meaning that you will end up with twice the space of the two disk RAID-1.
Maybe you are thinking of a different RAID level altogether? If speed is not the issue but you care about redundancy and fault tolerance, then you might want to look into RAID-5 or RAID-6, though these require quite a few disks.

Ello',

I'm continuously going to be adding drivers to the machine, not to the same raid-1 array. My plan is once space gets tight, I'll add another disk and bump it up to raid-5

alphaniner · 2013-08-13 13:06:51

You can't add capacity to any standard RAID without completely rebuilding it, ie. losing all your data. You might want to look into RAID-Z (ZFS), which can have capacity added without a rebuild. Maybe btrfs can do something similar.

cellisten · 2013-08-13 13:42:42

Btrfs does indeed have support for that:
https://btrfs.wiki.kernel.org/index.php … ew_devices

It needs to do balancing but that is not equivalent to a total rebuild.
What is the purpose of this RAID-ing anyway?

justdanyul · 2013-08-15 10:56:58

I'm sorry if I'm not being clear The question was completely about if anybody experienced problems (besides performance) in running a RAID-1 with two drive which has quite different performance

I'm really not too worried about being able to resize/grow the RAIDs. Its not a production system, its a personal box, so I'll just move everything to some external disks, delete the RAID-1, create a new RAID-5 , copy data back over and that's it

Arch Linux

#1 2013-08-12 10:34:47

Software RAID-1 with two different drives

#2 2013-08-12 14:18:11

Re: Software RAID-1 with two different drives

#3 2013-08-12 14:34:25

Re: Software RAID-1 with two different drives

#4 2013-08-13 12:35:29

Re: Software RAID-1 with two different drives

#5 2013-08-13 13:06:51

Re: Software RAID-1 with two different drives

#6 2013-08-13 13:42:42

Re: Software RAID-1 with two different drives

#7 2013-08-15 10:56:58

Re: Software RAID-1 with two different drives

Board footer