Migrating to software RAID

[lacerto]

Hi
I've got 2x250 gig SATA drives, one which I use just to backup data. I installed gentoo on one drive, but now reckon software mirror raid would be a really cute solution. However, given the amount of work that has gone into getting it right, I don't really want to re-install - it took weeks or more of tweaking to get where I am.

I'd like an identical partion layout, so was thinking of doing something like this:

1. Create images using dd of my partitions and save them on another computer
2. Create raid setup following this guide http://www.gentoo.org/doc/en/gentoo-x86-tipsntricks.xml
3. Copy back the images
4. Reboot

I'm just wondering if this would work, or am I being a simpleton and looking for trouble? Also, is there any performance hit by using software raid?

Any hints from anyone that can be bothered would be much appreciated.

L

[adaptr]

Make absolutely sure that you have modified your kernel and startup files before you attempt to mirror it!
Booting from a LiveCD to troubleshoot is not fun...

At a minimum, you need softraid (md) and raid-1 modules built into the kernel, changes to fstab and grub.conf, and you should install grub and its files on both drives physically.
This allows you to still boot from either drive should one of them fail.

Personally, I would never attempt this since it will cost you far too much data - unless you really intend to mirror every bit of data you download from the Internet.

I would mirror my system, which amounts to 10~15 GB at most, and my home partition, say another 25GB.
That leaves twice 200GB unmirrored for your data - over 400GB to use and abuse instead of the 200 you would have left if you mirrored that as well.

The setup changes not a bit, since the real partitions don't matter - the OS only works with the md* devices, which you can still name however you like.

As for performance - it sucks.

Which is another reason I would not use it for a desktop.
_________________
>>> emerge (3 of 7) mcse/70-293 to /
Essential tools: gentoolkit eix profuse screen

[lacerto]

Many thanks - didn't realise you could mirror just a partition or two.

My problem is that I've loads of data - mainly photos at 5+ mb each, and I'm terrified of loosing them.

But the idea of taking a performance hit is a concern and something I must research more - I've a pretty fast machine (4gig RAM, AMD64 4000) and would hate to loose too much speed - afterall, thats why aI bought the machine and am running gentoo!

[adaptr]

If performance is a prime concern, and you have a powerful machine (you do), I'd always try for a RAID-5 setup, since performance will scale nearly linearly, and redundancy is constant.
It will only cost you 1/3rd of your disk space, too - as opposed to mirroring the 250GB, which costs you half your space.
True, it will cost you another 250GB disk, but with 500GB of redundant disk space I doubt you'd run out any time soon...
_________________
>>> emerge (3 of 7) mcse/70-293 to /
Essential tools: gentoolkit eix profuse screen

[skoorbevad]

Why not take two disks and mirror them, and mount them on your filesystem somewhere? For instance, I have two external 200GB firewire drives hanging off my Mac Mini, and I'm using software RAID1 to mirror them and mount them up on /mnt/data. Anything I want to make sure I save (photos, mp3s, documents, etc.) I put it on this partition. Performance isn't such a big issue since nothing is actively using this partition for logging, swapping, or anything else -- after all, you're using using it as a data store.

Unless you have a legitimate need to mirror your ENTIRE filesystem, I would advise against it and just mount up a mirrored volume.